2019-01-24 18:08:25

by Cyrill Gorcunov

Subject: [PATCH -next] rcu: rcu_qs -- Use raise_softirq_irqoff to not save irqs twice

The rcu_qs is disabling IRQs by self so no need to do the same in raise_softirq,
instead we can save some cycles using raise_softirq_irqoff directly.

CC: Paul E. McKenney <[email protected]>
Signed-off-by: Cyrill Gorcunov <[email protected]>
---
kernel/rcu/tiny.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-next.git/kernel/rcu/tiny.c
===================================================================
--- linux-next.git.orig/kernel/rcu/tiny.c
+++ linux-next.git/kernel/rcu/tiny.c
@@ -65,7 +65,7 @@ void rcu_qs(void)
local_irq_save(flags);
if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
- raise_softirq(RCU_SOFTIRQ);
+ raise_softirq_irqoff(RCU_SOFTIRQ);
}
local_irq_restore(flags);
}
Subject: [PATCH]

2019-01-24 18:16:52

by Cyrill Gorcunov

Subject: [PATCH v2 -next] rcu: rcu_qs -- Use raise_softirq_irqoff to not save irqs twice

The rcu_qs is disabling IRQs by self so no need to do the same in raise_softirq
but instead we can save some cycles using raise_softirq_irqoff directly.

CC: Paul E. McKenney <[email protected]>
Signed-off-by: Cyrill Gorcunov <[email protected]>
---
The prev patch body has been screwed, sorry.

kernel/rcu/tiny.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-next.git/kernel/rcu/tiny.c
===================================================================
--- linux-next.git.orig/kernel/rcu/tiny.c
+++ linux-next.git/kernel/rcu/tiny.c
@@ -65,7 +65,7 @@ void rcu_qs(void)
local_irq_save(flags);
if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
- raise_softirq(RCU_SOFTIRQ);
+ raise_softirq_irqoff(RCU_SOFTIRQ);
}
local_irq_restore(flags);
}

2019-01-24 20:59:57

by Paul E. McKenney

Subject: Re: [PATCH v2 -next] rcu: rcu_qs -- Use raise_softirq_irqoff to not save irqs twice

On Thu, Jan 24, 2019 at 09:14:37PM +0300, Cyrill Gorcunov wrote:
> The rcu_qs is disabling IRQs by self so no need to do the same in raise_softirq
> but instead we can save some cycles using raise_softirq_irqoff directly.
>
> CC: Paul E. McKenney <[email protected]>
> Signed-off-by: Cyrill Gorcunov <[email protected]>

Good eyes, good combo optimization of both space and time, thank you!!!

Queued, most likely for v5.2.

Thanx, Paul

> ---
> The prev patch body has been screwed, sorry.
>
> kernel/rcu/tiny.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-next.git/kernel/rcu/tiny.c
> ===================================================================
> --- linux-next.git.orig/kernel/rcu/tiny.c
> +++ linux-next.git/kernel/rcu/tiny.c
> @@ -65,7 +65,7 @@ void rcu_qs(void)
> local_irq_save(flags);
> if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
> rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
> - raise_softirq(RCU_SOFTIRQ);
> + raise_softirq_irqoff(RCU_SOFTIRQ);
> }
> local_irq_restore(flags);
> }
>