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

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Date:   Fri, 04 Aug 2017 09:28:17 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        Eric Dumazet <eric.dumazet@...il.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

Peter Zijlstra <peterz@...radead.org> writes:
[snip]
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index 68123c1fe549..8d817cb80a38 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -14,13 +14,16 @@
>  #include <linux/llist.h>
>  
>  typedef void (*smp_call_func_t)(void *info);
> -struct call_single_data {
> +struct __call_single_data {
>  	struct llist_node llist;
>  	smp_call_func_t func;
>  	void *info;
>  	unsigned int flags;
>  };
>  
> +typedef struct __call_single_data call_single_data_t
> +	__aligned(sizeof(struct __call_single_data));
> +

Another requirement of the alignment is that it should be the power of
2.  Otherwise, for example, if someone adds a field to struct, so that
the size becomes 40 on x86_64.  The alignment should be 64 instead of
40.

Best Regards,
Huang, Ying

>  /* total number of cpus in this system (may exceed NR_CPUS) */
>  extern unsigned int total_cpus;
>  
[snip]