On (03/02/15 15:58), [email protected] wrote:
> ------------------------------------------------------
> From: Sergey Senozhatsky <[email protected]>
> Subject: cpumask: don't perform while loop in cpumask_next_and()
>
> cpumask_next_and() is looking for cpumask_next() in src1 in a loop and
> tests if found cpu is also present in src2. remove that loop, perform
> cpumask_and() of src1 and src2 first and use that new mask to find
> cpumask_next().
>
> Apart from removing while loop, ./bloat-o-meter on x86_64 shows
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-8 (-8)
> function old new delta
> cpumask_next_and 62 54 -8
>
Sir,
Please revert this commit.
It does awful things on really big machines (spotted by Peter Zijlstra).
-ss
> Signed-off-by: Sergey Senozhatsky <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: "David S. Miller" <[email protected]>
> Cc: Amir Vadai <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
> ---
>
> lib/cpumask.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff -puN lib/cpumask.c~cpumask-dont-perform-while-loop-in-cpumask_next_and
> lib/cpumask.c
> --- a/lib/cpumask.c~cpumask-dont-perform-while-loop-in-cpumask_next_and
> +++ a/lib/cpumask.c
> @@ -37,10 +37,11 @@ EXPORT_SYMBOL(__next_cpu_nr);
> int cpumask_next_and(int n, const struct cpumask *src1p,
> const struct cpumask *src2p)
> {
> - while ((n = cpumask_next(n, src1p)) < nr_cpu_ids)
> - if (cpumask_test_cpu(n, src2p))
> - break;
> - return n;
> + struct cpumask tmp;
> +
> + if (cpumask_and(&tmp, src1p, src2p))
> + return cpumask_next(n, &tmp);
> + return nr_cpu_ids;
> }
> EXPORT_SYMBOL(cpumask_next_and);
>
> _
>
> Patches currently in -mm which might be from [email protected] are
>
> cpumask-dont-perform-while-loop-in-cpumask_next_and.patch
> lib-lz4-pull-out-constant-tables.patch
>
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