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author | Jesper Dangaard Brouer <brouer@redhat.com> | 2023-01-20 15:07:43 +0300 |
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committer | Jakub Kicinski <kuba@kernel.org> | 2023-01-24 09:08:06 +0300 |
commit | 3176eb82681ec9c8af31c6588ddedcc6cfb9e445 (patch) | |
tree | abbec284deefc1b5e80f92bae0533ad453994788 /net/core/dev.c | |
parent | 695a376b59f72c249caad40da64d5cce239c5f48 (diff) | |
download | linux-3176eb82681ec9c8af31c6588ddedcc6cfb9e445.tar.xz |
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>
Diffstat (limited to 'net/core/dev.c')
-rw-r--r-- | net/core/dev.c | 5 |
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; |