linux-kernel - Re: [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single

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Message-ID: <20170802105321.3dettvyq4vmcvfth@hirez.programming.kicks-ass.net>
Date:   Wed, 2 Aug 2017 12:53:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "Huang, Ying" <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>, Aaron Lu <aaron.lu@...el.com>
Subject: Re: [PATCH 3/3] IPI: Avoid to use 2 cache lines for one
 call_single_data

On Wed, Aug 02, 2017 at 03:18:58AM -0700, Eric Dumazet wrote:
> What we can do instead is to force an alignment on 4*sizeof(void *).
> (32 bytes on 64bit, 16 bytes on 32bit arches)
> 
> Maybe something like this :
> 
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index 68123c1fe54918c051292eb5ba3427df09f31c2f..f7072bf173c5456e38e958d6af85a4793bced96e 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -19,7 +19,7 @@ struct call_single_data {
>  	smp_call_func_t func;
>  	void *info;
>  	unsigned int flags;
> -};
> +} __attribute__((aligned(4 * sizeof(void *))));

Agreed.