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net: make softnet_data.defer_count an atomic

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This is preparation work to remove the softnet_data.defer_lock,
as it is contended on hosts with large number of cores.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250928084934.3266948-2-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2025-09-28 08:49:32 +00:00 committed by Paolo Abeni
parent 2c0592bd5c
commit 9c94ae6bb0
3 changed files with 4 additions and 6 deletions
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2
include/linux/netdevice.h
View File

@ -3538,7 +3538,7 @@ struct softnet_data {
/* Another possibly contended cache line */
spinlock_t defer_lock ____cacheline_aligned_in_smp;
int defer_count;
atomic_t defer_count;
int defer_ipi_scheduled;
struct sk_buff *defer_list;
call_single_data_t defer_csd;

2
net/core/dev.c
View File

@ -6726,7 +6726,7 @@ static void skb_defer_free_flush(struct softnet_data *sd)
spin_lock(&sd->defer_lock);
skb = sd->defer_list;
sd->defer_list = NULL;
sd->defer_count = 0;
atomic_set(&sd->defer_count, 0);
spin_unlock(&sd->defer_lock);
while (skb != NULL) {

6
net/core/skbuff.c
View File

@ -7202,14 +7202,12 @@ nodefer: kfree_skb_napi_cache(skb);
sd = &per_cpu(softnet_data, cpu);
defer_max = READ_ONCE(net_hotdata.sysctl_skb_defer_max);
if (READ_ONCE(sd->defer_count) >= defer_max)
if (atomic_read(&sd->defer_count) >= defer_max)
goto nodefer;
spin_lock_bh(&sd->defer_lock);
/* Send an IPI every time queue reaches half capacity. */
kick = sd->defer_count == (defer_max >> 1);
/* Paired with the READ_ONCE() few lines above */
WRITE_ONCE(sd->defer_count, sd->defer_count + 1);
kick = (atomic_inc_return(&sd->defer_count) - 1) == (defer_max >> 1);
skb->next = sd->defer_list;
/* Paired with READ_ONCE() in skb_defer_free_flush() */