linux-kernel - Re: [PATCH 1/5] powerpc/mm: only call store_updates_sp() on stores in do_page

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Date:   Mon, 24 Apr 2017 14:40:27 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/5] powerpc/mm: only call store_updates_sp() on stores in do_page_fault()

Christophe Leroy <christophe.leroy@....fr> writes:

> Function store_updates_sp() checks whether the faulting
> instruction is a store updating r1. Therefore we can limit its calls
> to stores exceptions.
>
> This patch is an improvement of commit a7a9dcd882a67 ("powerpc: Avoid
> taking a data miss on every userspace instruction miss")
>
> With the same microbenchmark app, run with 500 as argument, on an
> MPC885 we get:
>
> Before this patch: 152000 DTLB misses
> After this patch:  147000 DTLB misses
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/mm/fault.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 3a7d580fdc59..67fefb59d40e 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -287,7 +287,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  	 * can result in fault, which will cause a deadlock when called with
>  	 * mmap_sem held
>  	 */
> -	if (!is_exec && user_mode(regs))
> +	if (is_write && user_mode(regs))
>  		store_update_sp = store_updates_sp(regs);
>  
>  	if (user_mode(regs))
> -- 
> 2.12.0