From: Nicholas Piggin <npiggin@gmail.com>
To: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v9] powerpc/mm: Only read faulting instruction when necessary in do_page_fault()
Date: Wed, 23 May 2018 19:36:59 +1000 [thread overview]
Message-ID: <20180523193659.03857d14@roar.ozlabs.ibm.com> (raw)
In-Reply-To: <3f8c7feadca2d52fa97c8feb5170c2ab67b6f992.1527065339.git.christophe.leroy@c-s.fr>
On Wed, 23 May 2018 10:53:22 +0200 (CEST)
Christophe Leroy <christophe.leroy@c-s.fr> wrote:
> Commit a7a9dcd882a67 ("powerpc: Avoid taking a data miss on every
> userspace instruction miss") has shown that limiting the read of
> faulting instruction to likely cases improves performance.
>
> This patch goes further into this direction by limiting the read
> of the faulting instruction to the only cases where it is likely
> needed.
>
> On an MPC885, with the same benchmark app as in the commit referred
> above, we see a reduction of about 3900 dTLB misses (approx 3%):
>
> Before the patch:
> Performance counter stats for './fault 500' (10 runs):
>
> 683033312 cpu-cycles ( +- 0.03% )
> 134538 dTLB-load-misses ( +- 0.03% )
> 46099 iTLB-load-misses ( +- 0.02% )
> 19681 faults ( +- 0.02% )
>
> 5.389747878 seconds time elapsed ( +- 0.06% )
>
> With the patch:
>
> Performance counter stats for './fault 500' (10 runs):
>
> 682112862 cpu-cycles ( +- 0.03% )
> 130619 dTLB-load-misses ( +- 0.03% )
> 46073 iTLB-load-misses ( +- 0.05% )
> 19681 faults ( +- 0.01% )
>
> 5.381342641 seconds time elapsed ( +- 0.07% )
>
> The proper work of the huge stack expansion was tested with the
> following app:
>
> int main(int argc, char **argv)
> {
> char buf[1024 * 1025];
>
> sprintf(buf, "Hello world !\n");
> printf(buf);
>
> exit(0);
> }
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Thanks,
Nick
next prev parent reply other threads:[~2018-05-23 9:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-23 8:53 [PATCH v9] powerpc/mm: Only read faulting instruction when necessary in do_page_fault() Christophe Leroy
2018-05-23 9:36 ` Nicholas Piggin [this message]
2018-05-25 11:41 ` [v9] " Michael Ellerman
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