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net: make softnet_data.dropped an atomic_t

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If under extreme cpu backlog pressure enqueue_to_backlog() has
to drop a packet, it could do this without dirtying a cache line
and potentially slowing down the target cpu.

Move sd->dropped into a separate cache line, and make it atomic.

In non pressure mode, this field is not touched, no need to consume
valuable space in a hot cache line.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2024-03-29 15:42:21 +00:00 committed by David S. Miller
parent 95e48d862a
commit a7ae7b0b2e
3 changed files with 13 additions and 6 deletions
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3
include/linux/netdevice.h
View File

@ -3237,10 +3237,11 @@ struct softnet_data {
unsigned int input_queue_tail;
#endif
unsigned int received_rps;
unsigned int dropped;
struct sk_buff_head input_pkt_queue;
struct napi_struct backlog;
atomic_t dropped ____cacheline_aligned_in_smp;
/* Another possibly contended cache line */
spinlock_t defer_lock ____cacheline_aligned_in_smp;
int defer_count;

13
net/core/dev.c
View File

@ -4800,17 +4800,22 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
struct softnet_data *sd;
unsigned long flags;
unsigned int qlen;
int max_backlog;
reason = SKB_DROP_REASON_DEV_READY;
if (!netif_running(skb->dev))
goto bad_dev;
reason = SKB_DROP_REASON_CPU_BACKLOG;
sd = &per_cpu(softnet_data, cpu);
qlen = skb_queue_len_lockless(&sd->input_pkt_queue);
max_backlog = READ_ONCE(net_hotdata.max_backlog);
if (unlikely(qlen > max_backlog))
goto cpu_backlog_drop;
backlog_lock_irq_save(sd, &flags);
qlen = skb_queue_len(&sd->input_pkt_queue);
if (qlen <= READ_ONCE(net_hotdata.max_backlog) &&
!skb_flow_limit(skb, qlen)) {
if (qlen <= max_backlog && !skb_flow_limit(skb, qlen)) {
if (qlen) {
enqueue:
__skb_queue_tail(&sd->input_pkt_queue, skb);
@ -4826,11 +4831,11 @@ enqueue:
napi_schedule_rps(sd);
goto enqueue;
}
reason = SKB_DROP_REASON_CPU_BACKLOG;
sd->dropped++;
backlog_unlock_irq_restore(sd, &flags);
cpu_backlog_drop:
atomic_inc(&sd->dropped);
bad_dev:
dev_core_stats_rx_dropped_inc(skb->dev);
kfree_skb_reason(skb, reason);

3
net/core/net-procfs.c
View File

@ -144,7 +144,8 @@ static int softnet_seq_show(struct seq_file *seq, void *v)
seq_printf(seq,
"%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x "
"%08x %08x\n",
sd->processed, sd->dropped, sd->time_squeeze, 0,
sd->processed, atomic_read(&sd->dropped),
sd->time_squeeze, 0,
0, 0, 0, 0, /* was fastroute */
0, /* was cpu_collision */
sd->received_rps, flow_limit_count,