Re: [PATCH 5/5] net: mvneta: reduce smp_processor_id() calling in mvneta_tx_done_gbe
From: Gregory CLEMENT <gregory.clement@bootlin.com>
Date: 2018-08-29 09:44:46
Also in:
linux-arm-kernel, lkml
Hi Jisheng, On mer., août 29 2018, Jisheng Zhang [off-list ref] wrote:
In the loop of mvneta_tx_done_gbe(), we call the smp_processor_id()
each time, move the call out of the loop to optimize the code a bit.
Before the patch, the loop looks like(under arm64):
ldr x1, [x29,#120]
...
ldr w24, [x1,#36]
...
bl 0 <_raw_spin_lock>
str w24, [x27,#132]
...
After the patch, the loop looks like(under arm64):
...
bl 0 <_raw_spin_lock>
str w23, [x28,#132]
...
where w23 is loaded so be ready before the loop.
From another side, mvneta_tx_done_gbe() is called from mvneta_poll()
which is in non-preemptible context, so it's safe to call the
smp_processor_id() function once.This improvement should go to net-next. Besides this patch looks nice: Reviewed-by: Gregory CLEMENT <gregory.clement@bootlin.com> Thanks, Gregory
quoted hunk
Signed-off-by: Jisheng Zhang <redacted> --- drivers/net/ethernet/marvell/mvneta.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c index 7d98f7828a30..62e81e267e13 100644 --- a/drivers/net/ethernet/marvell/mvneta.c +++ b/drivers/net/ethernet/marvell/mvneta.c@@ -2507,12 +2507,13 @@ static void mvneta_tx_done_gbe(struct mvneta_port *pp, u32 cause_tx_done) { struct mvneta_tx_queue *txq; struct netdev_queue *nq; + int cpu = smp_processor_id(); while (cause_tx_done) { txq = mvneta_tx_done_policy(pp, cause_tx_done); nq = netdev_get_tx_queue(pp->dev, txq->id); - __netif_tx_lock(nq, smp_processor_id()); + __netif_tx_lock(nq, cpu); if (txq->count) mvneta_txq_done(pp, txq);-- 2.18.0
-- Gregory Clement, Bootlin Embedded Linux and Kernel engineering http://bootlin.com