From 3176eb82681ec9c8af31c6588ddedcc6cfb9e445 Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Fri, 20 Jan 2023 13:07:43 +0100 Subject: [PATCH] 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 Signed-off-by: Jesper Dangaard Brouer Link: https://lore.kernel.org/r/167421646327.1321776.7390743166998776914.stgit@firesoul Signed-off-by: Jakub Kicinski --- net/core/dev.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index cf78f35..9c60190 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; -- 2.7.4