From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V4] arm64: percpu: Implement this_cpu operations
Date: Mon, 17 Nov 2014 10:40:11 +0000 [thread overview]
Message-ID: <20141117104010.GB18061@arm.com> (raw)
In-Reply-To: <1415977413-17642-1-git-send-email-steve.capper@linaro.org>
Hi Steve,
On Fri, Nov 14, 2014 at 03:03:33PM +0000, Steve Capper wrote:
> The generic this_cpu operations disable interrupts to ensure that the
> requested operation is protected from pre-emption. For arm64, this is
> overkill and can hurt throughput and latency.
>
> This patch provides arm64 specific implementations for the this_cpu
> operations. Rather than disable interrupts, we use the exclusive
> monitor or atomic operations as appropriate.
>
> The following operations are implemented: add, add_return, and, or,
> read, write, xchg. We also wire up a cmpxchg implementation from
> cmpxchg.h.
>
> Testing was performed using the percpu_test module and hackbench on a
> Juno board running 3.18-rc4.
Looks good. I notice that this change drops the compiler barriers too,
which we used to get via local_irq_{enable/disable}. I *think* that's fine
(at least, I couldn't find a place that breaks due to that) but it would be
nice to know that it was deliberate :)
> +static inline void __percpu_write(void *ptr, unsigned long val, int size)
> +{
> + switch (size) {
> + case 1:
> + ACCESS_ONCE(*((u8 *)ptr)) = (u8) val;
> + break;
> + case 2:
> + ACCESS_ONCE(*((u16 *)ptr)) = (u16) val;
> + break;
> + case 4:
> + ACCESS_ONCE(*((u32 *)ptr)) = (u32) val;
> + break;
> + case 8:
> + ACCESS_ONCE(*((u64 *)ptr)) = (u64) val;
> + break;
I think you've gone a bit overboard with brackets and spacing here. Can't
you just do something like:
ACCESS_ONCE(*(u64 *)ptr) = (u64)val;
Anyway:
Reviewed-by: Will Deacon <will.deacon@arm•com>
Will
next prev parent reply other threads:[~2014-11-17 10:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-06 11:12 [PATCH] arm64: percpu: Implement this_cpu operations Steve Capper
2014-11-06 11:26 ` Ard Biesheuvel
2014-11-06 11:52 ` Steve Capper
2014-11-06 12:23 ` [PATCH V2] " Steve Capper
2014-11-06 12:27 ` [PATCH] " Will Deacon
2014-11-07 13:52 ` Steve Capper
2014-11-14 11:37 ` [PATCH V3] " Steve Capper
2014-11-14 13:46 ` Will Deacon
2014-11-14 15:03 ` [PATCH V4] " Steve Capper
2014-11-17 10:40 ` Will Deacon [this message]
2014-11-19 15:49 ` Steve Capper
2014-11-19 16:53 ` [PATCH V5] " Steve Capper
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