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SubjectRe: [PATCH v9] powerpc/mm: Only read faulting instruction when necessary in do_page_fault()
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

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