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authorJesper Dangaard Brouer <brouer@redhat.com>2023-01-20 13:07:43 +0100
committerJakub Kicinski <kuba@kernel.org>2023-01-23 22:08:06 -0800
commit3176eb82681ec9c8af31c6588ddedcc6cfb9e445 (patch)
treeabbec284deefc1b5e80f92bae0533ad453994788
parent695a376b59f72c249caad40da64d5cce239c5f48 (diff)
net: avoid irqsave in skb_defer_free_flush
The spin_lock irqsave/restore API variant in skb_defer_free_flush can be replaced with the faster spin_lock irq variant, which doesn't need to read and restore the CPU flags. Using the unconditional irq "disable/enable" API variant is safe, because the skb_defer_free_flush() function is only called during NAPI-RX processing in net_rx_action(), where it is known the IRQs are enabled. Expected gain is 14 cycles from avoiding reading and restoring CPU flags in a spin_lock_irqsave/restore operation, measured via a microbencmark kernel module[1] on CPU E5-1650 v4 @ 3.60GHz. Microbenchmark overhead of spin_lock+unlock: - spin_lock_unlock_irq cost: 34 cycles(tsc) 9.486 ns - spin_lock_unlock_irqsave cost: 48 cycles(tsc) 13.567 ns We don't expect to see a measurable packet performance gain, as skb_defer_free_flush() is called infrequently once per NIC device NAPI bulk cycle and conditionally only if SKBs have been deferred by other CPUs via skb_attempt_defer_free(). [1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/time_bench_sample.c Reviewed-by: Jacob Keller <jacob.e.keller@intel.com> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Link: https://lore.kernel.org/r/167421646327.1321776.7390743166998776914.stgit@firesoul Signed-off-by: Jakub Kicinski <kuba@kernel.org>
-rw-r--r--net/core/dev.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index cf78f35bc0b9..9c60190fe352 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6616,17 +6616,16 @@ static int napi_threaded_poll(void *data)
static void skb_defer_free_flush(struct softnet_data *sd)
{
struct sk_buff *skb, *next;
- unsigned long flags;
/* Paired with WRITE_ONCE() in skb_attempt_defer_free() */
if (!READ_ONCE(sd->defer_list))
return;
- spin_lock_irqsave(&sd->defer_lock, flags);
+ spin_lock_irq(&sd->defer_lock);
skb = sd->defer_list;
sd->defer_list = NULL;
sd->defer_count = 0;
- spin_unlock_irqrestore(&sd->defer_lock, flags);
+ spin_unlock_irq(&sd->defer_lock);
while (skb != NULL) {
next = skb->next;