linux-kernel - Re: [PATCH bitmap-for-next 0/5] bitmap,cpumask: Add for_each_cpu

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Date:   Mon, 3 Oct 2022 11:52:07 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH bitmap-for-next 0/5] bitmap,cpumask: Add
 for_each_cpu_andnot()

On Mon, Oct 03, 2022 at 04:34:15PM +0100, Valentin Schneider wrote:
> As suggested by Yury, this is the bitmap/cpumask specific bits of [1]. This now
> also contains an extra fix for blk_mq.

Patches ##2-5 look good to me, but I'd like to give them some testing.
Let's also wait for other comments, and if nothing wrong will be spotted,
I'll take it.

Thanks,
Yury
 
> This is based on top of Yury's bitmap-for-next [2].
> 
> A note on treewide use of for_each_cpu_andnot()
> ===============================================
> 
> I've used the below coccinelle script to find places that could be patched (I
> couldn't figure out the valid syntax to patch from coccinelle itself):
> 
> ,-----
> @tmpandnot@
> expression tmpmask;
> iterator for_each_cpu;
> position p;
> statement S;
> @@
> cpumask_andnot(tmpmask, ...);
> 
> ...
> 
> (
> for_each_cpu@p(..., tmpmask, ...)
> 	S
> |
> for_each_cpu@p(..., tmpmask, ...)
> {
> 	...
> }
> )
> 
> @script:python depends on tmpandnot@
> p << tmpandnot.p;
> @@
> coccilib.report.print_report(p[0], "andnot loop here")
> '-----
> 
> Which yields (against c40e8341e3b3):
> 
> .//arch/powerpc/kernel/smp.c:1587:1-13: andnot loop here
> .//arch/powerpc/kernel/smp.c:1530:1-13: andnot loop here
> .//arch/powerpc/kernel/smp.c:1440:1-13: andnot loop here
> .//arch/powerpc/platforms/powernv/subcore.c:306:2-14: andnot loop here
> .//arch/x86/kernel/apic/x2apic_cluster.c:62:1-13: andnot loop here
> .//drivers/acpi/acpi_pad.c:110:1-13: andnot loop here
> .//drivers/cpufreq/armada-8k-cpufreq.c:148:1-13: andnot loop here
> .//drivers/cpufreq/powernv-cpufreq.c:931:1-13: andnot loop here
> .//drivers/net/ethernet/sfc/efx_channels.c:73:1-13: andnot loop here
> .//drivers/net/ethernet/sfc/siena/efx_channels.c:73:1-13: andnot loop here
> .//kernel/sched/core.c:345:1-13: andnot loop here
> .//kernel/sched/core.c:366:1-13: andnot loop here
> .//net/core/dev.c:3058:1-13: andnot loop here
> 
> A lot of those are actually of the shape
> 
>   for_each_cpu(cpu, mask) {
>       ...
>       cpumask_andnot(mask, ...);
>   }
> 
> I think *some* of the powerpc ones would be a match for for_each_cpu_andnot(),
> but I decided to just stick to the one obvious one in __sched_core_flip().
> 
> [1]: https://lore.kernel.org/all/20220923132527.1001870-1-vschneid@redhat.com/
> [2]: https://github.com/norov/linux.git/ -b bitmap-for-next
> 
> Cheers,
> Valentin
> 
> Valentin Schneider (5):
>   blk_mq: Fix cpumask_check() warning in blk_mq_hctx_next_cpu()
>   lib/find_bit: Introduce find_next_andnot_bit()
>   cpumask: Introduce for_each_cpu_andnot()
>   lib/test_cpumask: Add for_each_cpu_and(not) tests
>   sched/core: Merge cpumask_andnot()+for_each_cpu() into
>     for_each_cpu_andnot()
> 
>  block/blk-mq.c          |  9 +++++++--
>  include/linux/cpumask.h | 18 ++++++++++++++++++
>  include/linux/find.h    | 38 ++++++++++++++++++++++++++++++++++++++
>  kernel/sched/core.c     |  5 +----
>  lib/cpumask_kunit.c     | 19 +++++++++++++++++++
>  lib/find_bit.c          |  9 +++++++++
>  6 files changed, 92 insertions(+), 6 deletions(-)
> 
> --
> 2.31.1