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homa_outgoing.c
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homa_outgoing.c
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// SPDX-License-Identifier: BSD-2-Clause
/* This file contains functions related to the sender side of message
* transmission. It also contains utility functions for sending packets.
*/
#include "homa_impl.h"
#include "homa_peer.h"
#include "homa_rpc.h"
#include "homa_skb.h"
#include "homa_wire.h"
/**
* homa_message_out_init() - Initialize rpc->msgout.
* @rpc: RPC whose output message should be initialized.
* @length: Number of bytes that will eventually be in rpc->msgout.
*/
void homa_message_out_init(struct homa_rpc *rpc, int length)
{
rpc->msgout.length = length;
rpc->msgout.num_skbs = 0;
rpc->msgout.copied_from_user = 0;
rpc->msgout.packets = NULL;
rpc->msgout.next_xmit = &rpc->msgout.packets;
rpc->msgout.next_xmit_offset = 0;
atomic_set(&rpc->msgout.active_xmits, 0);
rpc->msgout.unscheduled = rpc->hsk->homa->unsched_bytes;
if (rpc->msgout.unscheduled > length)
rpc->msgout.unscheduled = length;
rpc->msgout.sched_priority = 0;
rpc->msgout.init_ns = sched_clock();
}
/**
* homa_fill_data_interleaved() - This function is invoked to fill in the
* part of a data packet after the initial header, when GSO is being used
* but TCP hijacking is not. As result, homa_seg_hdrs must be interleaved
* with the data to provide the correct offset for each segment.
* @rpc: RPC whose output message is being created.
* @skb: The packet being filled. The initial homa_data_hdr was
* created and initialized by the caller and the
* homa_skb_info has been filled in with the packet geometry.
* @iter: Describes location(s) of (remaining) message data in user
* space.
* Return: Either a negative errno or 0 (for success).
*/
int homa_fill_data_interleaved(struct homa_rpc *rpc, struct sk_buff *skb,
struct iov_iter *iter)
{
struct homa_skb_info *homa_info = homa_get_skb_info(skb);
int seg_length = homa_info->seg_length;
int bytes_left = homa_info->data_bytes;
int offset = homa_info->offset;
int err;
/* Each iteration of the following loop adds info for one packet,
* which includes a homa_seg_hdr followed by the data for that
* segment. The first homa_seg_hdr was already added by the caller.
*/
while (1) {
struct homa_seg_hdr seg;
if (bytes_left < seg_length)
seg_length = bytes_left;
err = homa_skb_append_from_iter(rpc->hsk->homa, skb, iter,
seg_length);
if (err != 0)
return err;
bytes_left -= seg_length;
offset += seg_length;
if (bytes_left == 0)
break;
seg.offset = htonl(offset);
err = homa_skb_append_to_frag(rpc->hsk->homa, skb, &seg,
sizeof(seg));
if (err != 0)
return err;
}
return 0;
}
/**
* homa_new_data_packet() - Allocate a new sk_buff and fill it with a Homa
* data packet. The resulting packet will be a GSO packet that will eventually
* be segmented by the NIC.
* @rpc: RPC that packet will belong to (msgout must have been
* initialized).
* @iter: Describes location(s) of (remaining) message data in user
* space.
* @offset: Offset in the message of the first byte of data in this
* packet.
* @length: How many bytes of data to include in the skb. Caller must
* ensure that this amount of data isn't too much for a
* well-formed GSO packet, and that iter has at least this
* much data.
* @max_seg_data: Maximum number of bytes of message data that can go in
* a single segment of the GSO packet.
* Return: A pointer to the new packet, or a negative errno.
*/
struct sk_buff *homa_new_data_packet(struct homa_rpc *rpc,
struct iov_iter *iter, int offset,
int length, int max_seg_data)
{
struct homa_skb_info *homa_info;
struct homa_data_hdr *h;
struct sk_buff *skb;
int err, gso_size;
__u64 segs;
segs = length + max_seg_data - 1;
do_div(segs, max_seg_data);
/* Initialize the overall skb. */
skb = homa_skb_new_tx(sizeof32(struct homa_data_hdr));
if (!skb)
return ERR_PTR(-ENOMEM);
/* Fill in the Homa header (which will be replicated in every
* network packet by GSO).
*/
h = (struct homa_data_hdr *)skb_put(skb, sizeof(struct homa_data_hdr));
h->common.sport = htons(rpc->hsk->port);
h->common.dport = htons(rpc->dport);
h->common.sequence = htonl(offset);
h->common.type = DATA;
homa_set_doff(h, sizeof(struct homa_data_hdr));
h->common.flags = HOMA_TCP_FLAGS;
h->common.checksum = 0;
h->common.urgent = htons(HOMA_TCP_URGENT);
h->common.sender_id = cpu_to_be64(rpc->id);
h->message_length = htonl(rpc->msgout.length);
h->incoming = htonl(rpc->msgout.unscheduled);
h->ack.client_id = 0;
homa_peer_get_acks(rpc->peer, 1, &h->ack);
h->cutoff_version = rpc->peer->cutoff_version;
h->retransmit = 0;
h->seg.offset = htonl(-1);
homa_info = homa_get_skb_info(skb);
homa_info->next_skb = NULL;
homa_info->wire_bytes = length + segs * (sizeof(struct homa_data_hdr)
+ rpc->hsk->ip_header_length + HOMA_ETH_OVERHEAD);
homa_info->data_bytes = length;
homa_info->seg_length = max_seg_data;
homa_info->offset = offset;
if (segs > 1 && rpc->hsk->sock.sk_protocol != IPPROTO_TCP) {
homa_set_doff(h, sizeof(struct homa_data_hdr) -
sizeof32(struct homa_seg_hdr));
h->seg.offset = htonl(offset);
gso_size = max_seg_data + sizeof(struct homa_seg_hdr);
err = homa_fill_data_interleaved(rpc, skb, iter);
} else {
gso_size = max_seg_data;
err = homa_skb_append_from_iter(rpc->hsk->homa, skb, iter,
length);
}
if (err)
goto error;
if (segs > 1) {
skb_shinfo(skb)->gso_segs = segs;
skb_shinfo(skb)->gso_size = gso_size;
/* It's unclear what gso_type should be used to force software
* GSO; the value below seems to work...
*/
skb_shinfo(skb)->gso_type =
rpc->hsk->homa->gso_force_software ? 0xd : SKB_GSO_TCPV6;
}
return skb;
error:
homa_skb_free_tx(rpc->hsk->homa, skb);
return ERR_PTR(err);
}
/**
* homa_message_out_fill() - Initializes information for sending a message
* for an RPC (either request or response); copies the message data from
* user space and (possibly) begins transmitting the message.
* @rpc: RPC for which to send message; this function must not
* previously have been called for the RPC. Must be locked. The RPC
* will be unlocked while copying data, but will be locked again
* before returning.
* @iter: Describes location(s) of message data in user space.
* @xmit: Nonzero means this method should start transmitting packets;
* transmission will be overlapped with copying from user space.
* Zero means the caller will initiate transmission after this
* function returns.
*
* Return: 0 for success, or a negative errno for failure. It is possible
* for the RPC to be freed while this function is active. If that
* happens, copying will cease, -EINVAL will be returned, and
* rpc->state will be RPC_DEAD.
*/
int homa_message_out_fill(struct homa_rpc *rpc, struct iov_iter *iter, int xmit)
__releases(rpc->bucket_lock)
__acquires(rpc->bucket_lock)
{
/* Geometry information for packets:
* mtu: largest size for an on-the-wire packet (including
* all headers through IP header, but not Ethernet
* header).
* max_seg_data: largest amount of Homa message data that fits
* in an on-the-wire packet (after segmentation).
* max_gso_data: largest amount of Homa message data that fits
* in a GSO packet (before segmentation).
*/
int mtu, max_seg_data, max_gso_data;
struct sk_buff **last_link;
struct dst_entry *dst;
__u64 segs_per_gso;
int overlap_xmit;
/* Bytes of the message that haven't yet been copied into skbs. */
int bytes_left;
int gso_size;
int err;
homa_message_out_init(rpc, iter->count);
if (unlikely(rpc->msgout.length > HOMA_MAX_MESSAGE_LENGTH ||
rpc->msgout.length == 0)) {
tt_record2("homa_message_out_fill found bad length %d for id %d",
rpc->msgout.length, rpc->id);
err = -EINVAL;
goto error;
}
/* Compute the geometry of packets. */
dst = homa_get_dst(rpc->peer, rpc->hsk);
mtu = dst_mtu(dst);
max_seg_data = mtu - rpc->hsk->ip_header_length
- sizeof(struct homa_data_hdr);
gso_size = dst->dev->gso_max_size;
if (gso_size > rpc->hsk->homa->max_gso_size)
gso_size = rpc->hsk->homa->max_gso_size;
/* Round gso_size down to an even # of mtus; calculation depends
* on whether we're doing TCP hijacking (need more space in TSO packet
* if no hijacking).
*/
if (rpc->hsk->sock.sk_protocol == IPPROTO_TCP) {
/* Hijacking */
segs_per_gso = gso_size - rpc->hsk->ip_header_length
- sizeof(struct homa_data_hdr);
do_div(segs_per_gso, max_seg_data);
} else {
/* No hijacking */
segs_per_gso = gso_size - rpc->hsk->ip_header_length -
sizeof(struct homa_data_hdr) +
sizeof(struct homa_seg_hdr);
do_div(segs_per_gso, max_seg_data +
sizeof(struct homa_seg_hdr));
}
if (segs_per_gso == 0)
segs_per_gso = 1;
max_gso_data = segs_per_gso * max_seg_data;
UNIT_LOG("; ", "mtu %d, max_seg_data %d, max_gso_data %d",
mtu, max_seg_data, max_gso_data);
overlap_xmit = rpc->msgout.length > 2 * max_gso_data;
rpc->msgout.granted = rpc->msgout.unscheduled;
atomic_or(RPC_COPYING_FROM_USER, &rpc->flags);
homa_skb_stash_pages(rpc->hsk->homa, rpc->msgout.length);
/* Each iteration of the loop below creates one GSO packet. */
tt_record3("starting copy from user space for id %d, length %d, unscheduled %d",
rpc->id, rpc->msgout.length, rpc->msgout.unscheduled);
last_link = &rpc->msgout.packets;
for (bytes_left = rpc->msgout.length; bytes_left > 0; ) {
int skb_data_bytes, offset;
struct sk_buff *skb;
homa_rpc_unlock(rpc);
skb_data_bytes = max_gso_data;
offset = rpc->msgout.length - bytes_left;
if (offset < rpc->msgout.unscheduled &&
(offset + skb_data_bytes) > rpc->msgout.unscheduled) {
/* Insert a packet boundary at the unscheduled limit,
* so we don't transmit extra data.
*/
skb_data_bytes = rpc->msgout.unscheduled - offset;
}
if (skb_data_bytes > bytes_left)
skb_data_bytes = bytes_left;
skb = homa_new_data_packet(rpc, iter, offset, skb_data_bytes,
max_seg_data);
if (unlikely(!skb)) {
err = PTR_ERR(skb);
homa_rpc_lock(rpc, "homa_message_out_fill");
goto error;
}
bytes_left -= skb_data_bytes;
homa_rpc_lock(rpc, "homa_message_out_fill2");
if (rpc->state == RPC_DEAD) {
/* RPC was freed while we were copying. */
err = -EINVAL;
homa_skb_free_tx(rpc->hsk->homa, skb);
goto error;
}
*last_link = skb;
last_link = &(homa_get_skb_info(skb)->next_skb);
*last_link = NULL;
rpc->msgout.num_skbs++;
rpc->msgout.copied_from_user = rpc->msgout.length - bytes_left;
if (overlap_xmit && list_empty(&rpc->throttled_links) &&
xmit && offset < rpc->msgout.granted) {
tt_record1("waking up pacer for id %d", rpc->id);
homa_add_to_throttled(rpc);
}
}
tt_record2("finished copy from user space for id %d, length %d",
rpc->id, rpc->msgout.length);
atomic_andnot(RPC_COPYING_FROM_USER, &rpc->flags);
INC_METRIC(sent_msg_bytes, rpc->msgout.length);
if (!overlap_xmit && xmit)
homa_xmit_data(rpc, false);
return 0;
error:
atomic_andnot(RPC_COPYING_FROM_USER, &rpc->flags);
return err;
}
/**
* homa_xmit_control() - Send a control packet to the other end of an RPC.
* @type: Packet type, such as DATA.
* @contents: Address of buffer containing the contents of the packet.
* Only information after the common header must be valid;
* the common header will be filled in by this function.
* @length: Length of @contents (including the common header).
* @rpc: The packet will go to the socket that handles the other end
* of this RPC. Addressing info for the packet, including all of
* the fields of homa_common_hdr except type, will be set from this.
*
* Return: Either zero (for success), or a negative errno value if there
* was a problem.
*/
int homa_xmit_control(enum homa_packet_type type, void *contents,
size_t length, struct homa_rpc *rpc)
{
struct homa_common_hdr *h = contents;
h->type = type;
h->sport = htons(rpc->hsk->port);
h->dport = htons(rpc->dport);
h->flags = HOMA_TCP_FLAGS;
h->urgent = htons(HOMA_TCP_URGENT);
h->sender_id = cpu_to_be64(rpc->id);
return __homa_xmit_control(contents, length, rpc->peer, rpc->hsk);
}
/**
* __homa_xmit_control() - Lower-level version of homa_xmit_control: sends
* a control packet.
* @contents: Address of buffer containing the contents of the packet.
* The caller must have filled in all of the information,
* including the common header.
* @length: Length of @contents.
* @peer: Destination to which the packet will be sent.
* @hsk: Socket via which the packet will be sent.
*
* Return: Either zero (for success), or a negative errno value if there
* was a problem.
*/
int __homa_xmit_control(void *contents, size_t length, struct homa_peer *peer,
struct homa_sock *hsk)
{
#ifndef __STRIP__ /* See strip.py */
struct netdev_queue *txq;
#endif /* See strip.py */
struct homa_common_hdr *h;
struct dst_entry *dst;
int result, priority;
struct sk_buff *skb;
int extra_bytes;
dst = homa_get_dst(peer, hsk);
skb = homa_skb_new_tx(HOMA_MAX_HEADER);
if (unlikely(!skb))
return -ENOBUFS;
dst_hold(dst);
skb_dst_set(skb, dst);
h = skb_put(skb, length);
memcpy(h, contents, length);
extra_bytes = HOMA_MIN_PKT_LENGTH - length;
if (extra_bytes > 0) {
memset(skb_put(skb, extra_bytes), 0, extra_bytes);
UNIT_LOG(",", "padded control packet with %d bytes",
extra_bytes);
}
priority = hsk->homa->num_priorities - 1;
skb->ooo_okay = 1;
skb_get(skb);
if (hsk->inet.sk.sk_family == AF_INET6) {
result = ip6_xmit(&hsk->inet.sk, skb, &peer->flow.u.ip6, 0,
NULL, hsk->homa->priority_map[priority] << 4,
0);
} else {
/* This will find its way to the DSCP field in the IPv4 hdr. */
hsk->inet.tos = hsk->homa->priority_map[priority] << 5;
result = ip_queue_xmit(&hsk->inet.sk, skb, &peer->flow);
}
if (unlikely(result != 0)) {
INC_METRIC(control_xmit_errors, 1);
/* It appears that ip*_xmit frees skbuffs after
* errors; the following code is to raise an alert if
* this isn't actually the case. The extra skb_get above
* and kfree_skb call below are needed to do the check
* accurately (otherwise the buffer could be freed and
* its memory used for some other purpose, resulting in
* a bogus "reference count").
*/
if (refcount_read(&skb->users) > 1) {
#ifndef __STRIP__ /* See strip.py */
if (hsk->inet.sk.sk_family == AF_INET6) {
pr_notice("ip6_xmit didn't free Homa control packet (type %d) after error %d\n",
h->type, result);
} else {
pr_notice("ip_queue_xmit didn't free Homa control packet (type %d) after error %d\n",
h->type, result);
tt_record2("ip_queue_xmit didn't free Homa control packet (type %d) after error %d\n",
h->type, result);
}
#else /* See strip.py */
if (hsk->inet.sk.sk_family == AF_INET6)
pr_notice("ip6_xmit didn't free Homa control packet (type %d) after error %d\n",
h->type, result);
else
pr_notice("ip_queue_xmit didn't free Homa control packet (type %d) after error %d\n",
h->type, result);
#endif /* See strip.py */
}
}
#ifndef __STRIP__ /* See strip.py */
txq = netdev_get_tx_queue(skb->dev, skb->queue_mapping);
if (netif_tx_queue_stopped(txq))
tt_record4("__homa_xmit_control found stopped txq for id %d, qid %d, num_queued %d, limit %d",
be64_to_cpu(h->sender_id), skb->queue_mapping,
txq->dql.num_queued, txq->dql.adj_limit);
#endif /* See strip.py */
INC_METRIC(packets_sent[h->type - DATA], 1);
INC_METRIC(priority_bytes[priority], skb->len);
INC_METRIC(priority_packets[priority], 1);
kfree_skb(skb);
return result;
}
/**
* homa_xmit_unknown() - Send an UNKNOWN packet to a peer.
* @skb: Buffer containing an incoming packet; identifies the peer to
* which the UNKNOWN packet should be sent.
* @hsk: Socket that should be used to send the UNKNOWN packet.
*/
void homa_xmit_unknown(struct sk_buff *skb, struct homa_sock *hsk)
{
struct homa_common_hdr *h = (struct homa_common_hdr *)skb->data;
struct in6_addr saddr = skb_canonical_ipv6_saddr(skb);
struct homa_unknown_hdr unknown;
struct homa_peer *peer;
if (hsk->homa->verbose)
pr_notice("sending UNKNOWN to peer %s:%d for id %llu",
homa_print_ipv6_addr(&saddr),
ntohs(h->sport), homa_local_id(h->sender_id));
tt_record3("sending unknown to 0x%x:%d for id %llu",
tt_addr(saddr), ntohs(h->sport),
homa_local_id(h->sender_id));
unknown.common.sport = h->dport;
unknown.common.dport = h->sport;
unknown.common.type = UNKNOWN;
unknown.common.flags = HOMA_TCP_FLAGS;
unknown.common.urgent = htons(HOMA_TCP_URGENT);
unknown.common.sender_id = cpu_to_be64(homa_local_id(h->sender_id));
peer = homa_peer_find(hsk->homa->peers, &saddr, &hsk->inet);
if (!IS_ERR(peer))
__homa_xmit_control(&unknown, sizeof(unknown), peer, hsk);
}
/**
* homa_xmit_data() - If an RPC has outbound data packets that are permitted
* to be transmitted according to the scheduling mechanism, arrange for
* them to be sent (some may be sent immediately; others may be sent
* later by the pacer thread).
* @rpc: RPC to check for transmittable packets. Must be locked by
* caller. Note: this function will release the RPC lock while
* passing packets through the RPC stack, then reacquire it
* before returning. It is possible that the RPC gets freed
* when the lock isn't held, in which case the state will
* be RPC_DEAD on return.
* @force: True means send at least one packet, even if the NIC queue
* is too long. False means that zero packets may be sent, if
* the NIC queue is sufficiently long.
*/
void homa_xmit_data(struct homa_rpc *rpc, bool force)
__releases(rpc->bucket_lock)
__acquires(rpc->bucket_lock)
{
struct homa *homa = rpc->hsk->homa;
#ifndef __STRIP__ /* See strip.py */
struct netdev_queue *txq;
#endif /* See strip.py */
atomic_inc(&rpc->msgout.active_xmits);
while (*rpc->msgout.next_xmit) {
int priority;
struct sk_buff *skb = *rpc->msgout.next_xmit;
if (rpc->msgout.next_xmit_offset >= rpc->msgout.granted) {
tt_record3("homa_xmit_data stopping at offset %d for id %u: granted is %d",
rpc->msgout.next_xmit_offset, rpc->id,
rpc->msgout.granted);
break;
}
if ((rpc->msgout.length - rpc->msgout.next_xmit_offset)
>= homa->throttle_min_bytes) {
if (!homa_check_nic_queue(homa, skb, force)) {
tt_record1("homa_xmit_data adding id %u to throttle queue",
rpc->id);
homa_add_to_throttled(rpc);
break;
}
}
if (rpc->msgout.next_xmit_offset < rpc->msgout.unscheduled) {
priority = homa_unsched_priority(homa, rpc->peer,
rpc->msgout.length);
} else {
priority = rpc->msgout.sched_priority;
}
rpc->msgout.next_xmit = &(homa_get_skb_info(skb)->next_skb);
rpc->msgout.next_xmit_offset +=
homa_get_skb_info(skb)->data_bytes;
homa_rpc_unlock(rpc);
skb_get(skb);
__homa_xmit_data(skb, rpc, priority);
#ifndef __STRIP__ /* See strip.py */
txq = netdev_get_tx_queue(skb->dev, skb->queue_mapping);
if (netif_tx_queue_stopped(txq))
tt_record4("homa_xmit_data found stopped txq for id %d, qid %d, num_queued %d, limit %d",
rpc->id, skb->queue_mapping,
txq->dql.num_queued, txq->dql.adj_limit);
#endif /* See strip.py */
force = false;
homa_rpc_lock(rpc, "homa_xmit_data");
if (rpc->state == RPC_DEAD)
break;
}
atomic_dec(&rpc->msgout.active_xmits);
}
/**
* __homa_xmit_data() - Handles packet transmission stuff that is common
* to homa_xmit_data and homa_resend_data.
* @skb: Packet to be sent. The packet will be freed after transmission
* (and also if errors prevented transmission).
* @rpc: Information about the RPC that the packet belongs to.
* @priority: Priority level at which to transmit the packet.
*/
void __homa_xmit_data(struct sk_buff *skb, struct homa_rpc *rpc, int priority)
{
#ifndef __STRIP__ /* See strip.py */
struct homa_skb_info *homa_info = homa_get_skb_info(skb);
#endif /* See strip.py */
struct dst_entry *dst;
int err;
/* Update info that may have changed since the message was initially
* created.
*/
((struct homa_data_hdr *)skb_transport_header(skb))->cutoff_version =
rpc->peer->cutoff_version;
dst = homa_get_dst(rpc->peer, rpc->hsk);
dst_hold(dst);
skb_dst_set(skb, dst);
skb->ooo_okay = 1;
skb->ip_summed = CHECKSUM_PARTIAL;
skb->csum_start = skb_transport_header(skb) - skb->head;
skb->csum_offset = offsetof(struct homa_common_hdr, checksum);
if (rpc->hsk->inet.sk.sk_family == AF_INET6) {
tt_record4("calling ip6_xmit: wire_bytes %d, peer 0x%x, id %d, offset %d",
homa_get_skb_info(skb)->wire_bytes,
tt_addr(rpc->peer->addr), rpc->id,
homa_info->offset);
err = ip6_xmit(&rpc->hsk->inet.sk, skb, &rpc->peer->flow.u.ip6,
0, NULL,
rpc->hsk->homa->priority_map[priority] << 4, 0);
} else {
tt_record4("calling ip_queue_xmit: wire_bytes %d, peer 0x%x, id %d, offset %d",
homa_get_skb_info(skb)->wire_bytes,
tt_addr(rpc->peer->addr), rpc->id,
homa_info->offset);
rpc->hsk->inet.tos =
rpc->hsk->homa->priority_map[priority] << 5;
err = ip_queue_xmit(&rpc->hsk->inet.sk, skb, &rpc->peer->flow);
}
tt_record4("Finished queueing packet: rpc id %llu, offset %d, len %d, qid %d",
rpc->id, homa_info->offset,
homa_get_skb_info(skb)->data_bytes, skb->queue_mapping);
if (err)
INC_METRIC(data_xmit_errors, 1);
INC_METRIC(packets_sent[0], 1);
INC_METRIC(priority_bytes[priority], skb->len);
INC_METRIC(priority_packets[priority], 1);
}
/**
* homa_resend_data() - This function is invoked as part of handling RESEND
* requests. It retransmits the packet(s) containing a given range of bytes
* from a message.
* @rpc: RPC for which data should be resent.
* @start: Offset within @rpc->msgout of the first byte to retransmit.
* @end: Offset within @rpc->msgout of the byte just after the last one
* to retransmit.
* @priority: Priority level to use for the retransmitted data packets.
*/
void homa_resend_data(struct homa_rpc *rpc, int start, int end,
int priority)
{
struct homa_skb_info *homa_info;
struct sk_buff *skb;
if (end <= start)
return;
/* Each iteration of this loop checks one packet in the message
* to see if it contains segments that need to be retransmitted.
*/
for (skb = rpc->msgout.packets; skb; skb = homa_info->next_skb) {
int seg_offset, offset, seg_length, data_left;
struct homa_data_hdr *h;
homa_info = homa_get_skb_info(skb);
offset = homa_info->offset;
if (offset >= end)
break;
if (start >= (offset + homa_info->data_bytes))
continue;
offset = homa_info->offset;
seg_offset = sizeof32(struct homa_data_hdr);
data_left = homa_info->data_bytes;
if (skb_shinfo(skb)->gso_segs <= 1) {
seg_length = data_left;
} else {
seg_length = homa_info->seg_length;
h = (struct homa_data_hdr *)skb_transport_header(skb);
}
for ( ; data_left > 0; data_left -= seg_length,
offset += seg_length,
seg_offset += skb_shinfo(skb)->gso_size) {
struct homa_skb_info *new_homa_info;
struct sk_buff *new_skb;
int err;
if (seg_length > data_left)
seg_length = data_left;
if (end <= offset)
goto resend_done;
if ((offset + seg_length) <= start)
continue;
/* This segment must be retransmitted. */
new_skb = homa_skb_new_tx(sizeof(struct homa_data_hdr)
- sizeof(struct homa_seg_hdr));
if (unlikely(!new_skb)) {
if (rpc->hsk->homa->verbose)
pr_notice("%s couldn't allocate skb\n",
__func__);
UNIT_LOG("; ", "skb allocation error");
goto resend_done;
}
h = __skb_put_data(new_skb, skb_transport_header(skb),
sizeof32(struct homa_data_hdr));
h->common.sequence = htonl(offset);
h->seg.offset = htonl(offset);
h->retransmit = 1;
if ((offset + seg_length) <= rpc->msgout.granted)
h->incoming = htonl(rpc->msgout.granted);
else if ((offset + seg_length) > rpc->msgout.length)
h->incoming = htonl(rpc->msgout.length);
else
h->incoming = htonl(offset + seg_length);
err = homa_skb_append_from_skb(rpc->hsk->homa, new_skb,
skb, seg_offset,
seg_length);
if (err != 0) {
pr_err("%s got error %d from homa_skb_append_from_skb\n",
__func__, err);
UNIT_LOG("; ", "%s got error %d while copying data",
__func__, -err);
kfree_skb(new_skb);
goto resend_done;
}
new_homa_info = homa_get_skb_info(new_skb);
new_homa_info->wire_bytes = rpc->hsk->ip_header_length
+ sizeof(struct homa_data_hdr)
+ seg_length + HOMA_ETH_OVERHEAD;
new_homa_info->data_bytes = seg_length;
new_homa_info->seg_length = seg_length;
new_homa_info->offset = offset;
tt_record3("retransmitting offset %d, length %d, id %d",
offset, seg_length, rpc->id);
homa_check_nic_queue(rpc->hsk->homa, new_skb, true);
__homa_xmit_data(new_skb, rpc, priority);
INC_METRIC(resent_packets, 1);
}
}
resend_done:
return;
}
/**
* homa_outgoing_sysctl_changed() - Invoked whenever a sysctl value is changed;
* any output-related parameters that depend on sysctl-settable values.
* @homa: Overall data about the Homa protocol implementation.
*/
void homa_outgoing_sysctl_changed(struct homa *homa)
{
__u64 tmp;
tmp = 8 * 1000ULL * 1000ULL * 1000ULL;
/* Underestimate link bandwidth (overestimate time) by 1%. */
tmp = tmp * 101 / 100;
do_div(tmp, homa->link_mbps);
homa->ns_per_mbyte = tmp;
}
/**
* homa_check_nic_queue() - This function is invoked before passing a packet
* to the NIC for transmission. It serves two purposes. First, it maintains
* an estimate of the NIC queue length. Second, it indicates to the caller
* whether the NIC queue is so full that no new packets should be queued
* (Homa's SRPT depends on keeping the NIC queue short).
* @homa: Overall data about the Homa protocol implementation.
* @skb: Packet that is about to be transmitted.
* @force: True means this packet is going to be transmitted
* regardless of the queue length.
* Return: Nonzero is returned if either the NIC queue length is
* acceptably short or @force was specified. 0 means that the
* NIC queue is at capacity or beyond, so the caller should delay
* the transmission of @skb. If nonzero is returned, then the
* queue estimate is updated to reflect the transmission of @skb.
*/
int homa_check_nic_queue(struct homa *homa, struct sk_buff *skb, bool force)
{
__u64 idle, new_idle, clock, ns_for_packet;
int bytes;
bytes = homa_get_skb_info(skb)->wire_bytes;
ns_for_packet = homa->ns_per_mbyte;
ns_for_packet *= bytes;
do_div(ns_for_packet, 1000000);
while (1) {
clock = sched_clock();
idle = atomic64_read(&homa->link_idle_time);
if ((clock + homa->max_nic_queue_ns) < idle && !force &&
!(homa->flags & HOMA_FLAG_DONT_THROTTLE))
return 0;
if (!list_empty(&homa->throttled_rpcs))
INC_METRIC(pacer_bytes, bytes);
#ifndef __STRIP__ /* See strip.py */
if (idle < clock) {
if (homa->pacer_wake_time) {
__u64 lost = (homa->pacer_wake_time > idle)
? clock - homa->pacer_wake_time
: clock - idle;
INC_METRIC(pacer_lost_ns, lost);
tt_record1("pacer lost %d cycles", lost);
}
new_idle = clock + ns_for_packet;
} else {
new_idle = idle + ns_for_packet;
}
#else /* See strip.py */
if (idle < clock)
new_idle = clock + ns_for_packet;
else
new_idle = idle + ns_for_packet;
#endif /* See strip.py */
/* This method must be thread-safe. */
if (atomic64_cmpxchg_relaxed(&homa->link_idle_time, idle,
new_idle) == idle)
break;
}
return 1;
}
/**
* homa_pacer_main() - Top-level function for the pacer thread.
* @transport: Pointer to struct homa.
*
* Return: Always 0.
*/
int homa_pacer_main(void *transport)
{
struct homa *homa = (struct homa *)transport;
homa->pacer_wake_time = sched_clock();
while (1) {
if (homa->pacer_exit) {
homa->pacer_wake_time = 0;
break;
}
homa_pacer_xmit(homa);
/* Sleep this thread if the throttled list is empty. Even
* if the throttled list isn't empty, call the scheduler
* to give other processes a chance to run (if we don't,
* softirq handlers can get locked out, which prevents
* incoming packets from being handled).
*/
set_current_state(TASK_INTERRUPTIBLE);
#ifndef __STRIP__ /* See strip.py */
if (list_first_or_null_rcu(&homa->throttled_rpcs,
struct homa_rpc, throttled_links) == NULL)
tt_record("pacer sleeping");
else
#else /* See strip.py */
if (list_first_or_null_rcu(&homa->throttled_rpcs,
struct homa_rpc,
throttled_links) != NULL)
#endif /* See strip.py */
__set_current_state(TASK_RUNNING);
INC_METRIC(pacer_ns, sched_clock() - homa->pacer_wake_time);
homa->pacer_wake_time = 0;
schedule();
homa->pacer_wake_time = sched_clock();
__set_current_state(TASK_RUNNING);
}
kthread_complete_and_exit(&homa_pacer_kthread_done, 0);
return 0;
}
/**
* homa_pacer_xmit() - Transmit packets from the throttled list. Note:
* this function may be invoked from either process context or softirq (BH)
* level. This function is invoked from multiple places, not just in the
* pacer thread. The reason for this is that (as of 10/2019) Linux's scheduling
* of the pacer thread is unpredictable: the thread may block for long periods
* of time (e.g., because it is assigned to the same CPU as a busy interrupt
* handler). This can result in poor utilization of the network link. So,
* this method gets invoked from other places as well, to increase the
* likelihood that we keep the link busy. Those other invocations are not
* guaranteed to happen, so the pacer thread provides a backstop.
* @homa: Overall data about the Homa protocol implementation.
*/
void homa_pacer_xmit(struct homa *homa)
{
struct homa_rpc *rpc;
int i;
/* Make sure only one instance of this function executes at a
* time.
*/
if (!spin_trylock_bh(&homa->pacer_mutex))
return;
/* Each iteration through the following loop sends one packet. We
* limit the number of passes through this loop in order to cap the
* time spent in one call to this function (see note in
* homa_pacer_main about interfering with softirq handlers).
*/
for (i = 0; i < 5; i++) {
__u64 idle_time, now;
/* If the NIC queue is too long, wait until it gets shorter. */
now = sched_clock();
idle_time = atomic64_read(&homa->link_idle_time);
while ((now + homa->max_nic_queue_ns) < idle_time) {
/* If we've xmitted at least one packet then
* return (this helps with testing and also
* allows homa_pacer_main to yield the core).
*/
if (i != 0)
goto done;
now = sched_clock();
}
/* Note: when we get here, it's possible that the NIC queue is
* still too long because other threads have queued packets,
* but we transmit anyway so we don't starve (see perf.text
* for more info).
*/
/* Lock the first throttled RPC. This may not be possible
* because we have to hold throttle_lock while locking
* the RPC; that means we can't wait for the RPC lock because
* of lock ordering constraints (see sync.txt). Thus, if
* the RPC lock isn't available, do nothing. Holding the
* throttle lock while locking the RPC is important because
* it keeps the RPC from being deleted before it can be locked.
*/
homa_throttle_lock(homa);
homa->pacer_fifo_count -= homa->pacer_fifo_fraction;
if (homa->pacer_fifo_count <= 0) {
struct homa_rpc *cur;
__u64 oldest = ~0;
homa->pacer_fifo_count += 1000;
rpc = NULL;
list_for_each_entry_rcu(cur, &homa->throttled_rpcs,
throttled_links) {
if (cur->msgout.init_ns < oldest) {
rpc = cur;
oldest = cur->msgout.init_ns;
}
}
} else {
rpc = list_first_or_null_rcu(&homa->throttled_rpcs,
struct homa_rpc,
throttled_links);
}
if (!rpc) {
homa_throttle_unlock(homa);
break;
}
if (!homa_rpc_try_lock(rpc, "homa_pacer_xmit")) {
homa_throttle_unlock(homa);
INC_METRIC(pacer_skipped_rpcs, 1);
break;
}
homa_throttle_unlock(homa);
tt_record4("pacer calling homa_xmit_data for rpc id %llu, port %d, offset %d, bytes_left %d",
rpc->id, rpc->hsk->port,
rpc->msgout.next_xmit_offset,
rpc->msgout.length - rpc->msgout.next_xmit_offset);
homa_xmit_data(rpc, true);
/* Note: rpc->state could be RPC_DEAD here, but the code
* below should work anyway.
*/
if (!*rpc->msgout.next_xmit || rpc->msgout.next_xmit_offset >=
rpc->msgout.granted) {
/* Nothing more to transmit from this message (right
* now), so remove it from the throttled list.
*/
homa_throttle_lock(homa);
if (!list_empty(&rpc->throttled_links)) {
tt_record2("pacer removing id %d from throttled list, offset %d",
rpc->id, rpc->msgout.next_xmit_offset);
list_del_rcu(&rpc->throttled_links);
if (list_empty(&homa->throttled_rpcs))
INC_METRIC(throttled_ns, sched_clock()
- homa->throttle_add);
/* Note: this reinitialization is only safe
* because the pacer only looks at the first
* element of the list, rather than traversing
* it (and besides, we know the pacer isn't
* active concurrently, since this code *is*
* the pacer). It would not be safe under more
* general usage patterns.
*/
INIT_LIST_HEAD_RCU(&rpc->throttled_links);
}
homa_throttle_unlock(homa);
}
homa_rpc_unlock(rpc);
}
done:
spin_unlock_bh(&homa->pacer_mutex);
}
/**
* homa_pacer_stop() - Will cause the pacer thread to exit (waking it up
* if necessary); doesn't return until after the pacer thread has exited.
* @homa: Overall data about the Homa protocol implementation.
*/
void homa_pacer_stop(struct homa *homa)
{
homa->pacer_exit = true;
wake_up_process(homa->pacer_kthread);
kthread_stop(homa->pacer_kthread);
homa->pacer_kthread = NULL;
}
/**
* homa_add_to_throttled() - Make sure that an RPC is on the throttled list
* and wake up the pacer thread if necessary.
* @rpc: RPC with outbound packets that have been granted but can't be
* sent because of NIC queue restrictions. Must be locked by caller.