From: Helge Deller <deller@gmx.de>
To: John David Anglin <dave.anglin@bell.net>,
linux-parisc@vger.kernel.org,
James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: Re: [PATCH] parisc: Optimize switch_mm
Date: Wed, 26 Jul 2017 20:02:52 +0200 [thread overview]
Message-ID: <20170726180252.GA1129@p100.box> (raw)
In-Reply-To: <16F63B59-7A36-48F0-A5C7-670CA2ED9DED@bell.net>
* John David Anglin <dave.anglin@bell.net>:
> We only need to switch contexts when prev != next, and we don't need to disable interrupts
> to do the check.
>
> Signed-off-by: John David Anglin <dave.anglin@bell.net>
>
>
> diff --git a/arch/parisc/include/asm/mmu_context.h b/arch/parisc/include/asm/mmu_context.h
> index a81226257878..b1dc6e3f0dd0 100644
> --- a/arch/parisc/include/asm/mmu_context.h
> +++ b/arch/parisc/include/asm/mmu_context.h
> @@ -49,26 +49,19 @@ static inline void load_context(mm_context_t context)
> mtctl(__space_to_prot(context), 8);
> }
>
> -static inline void switch_mm_irqs_off(struct mm_struct *prev,
> +static inline void switch_mm(struct mm_struct *prev,
> struct mm_struct *next, struct task_struct *tsk)
> {
> + unsigned long flags;
> +
> if (prev != next) {
> + local_irq_save(flags);
> mtctl(__pa(next->pgd), 25);
> load_context(next->context);
> + local_irq_restore(flags);
> }
> }
>
> -static inline void switch_mm(struct mm_struct *prev,
> - struct mm_struct *next, struct task_struct *tsk)
> -{
> - unsigned long flags;
> -
> - local_irq_save(flags);
> - switch_mm_irqs_off(prev, next, tsk);
> - local_irq_restore(flags);
> -}
> -#define switch_mm_irqs_off switch_mm_irqs_off
> -
> #define deactivate_mm(tsk,mm) do { } while (0)
>
> static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
Instead I'd then suggest the patch below.
The if-clause in switch_mm_irqs_off() will then probably be optimized
away by the compiler.
diff --git a/arch/parisc/include/asm/mmu_context.h b/arch/parisc/include/asm/mmu_context.h
index a812262..e4a6570 100644
--- a/arch/parisc/include/asm/mmu_context.h
+++ b/arch/parisc/include/asm/mmu_context.h
@@ -63,6 +63,9 @@ static inline void switch_mm(struct mm_struct *prev,
{
unsigned long flags;
+ if (prev == next)
+ return;
+
local_irq_save(flags);
switch_mm_irqs_off(prev, next, tsk);
local_irq_restore(flags);
next prev parent reply other threads:[~2017-07-26 18:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-25 21:31 [PATCH] parisc: Optimize switch_mm John David Anglin
2017-07-26 18:02 ` Helge Deller [this message]
2017-07-26 18:49 ` John David Anglin
2017-07-26 19:13 ` Helge Deller
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