From: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
To: Yury Norov <yury.norov@gmail.com>
Cc: linux-kernel@vger.kernel.org,
"James E.J. Bottomley" <jejb@linux.ibm.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Alexey Klimov <aklimov@redhat.com>,
Amitkumar Karwar <amitkarwar@gmail.com>,
Andi Kleen <ak@linux.intel.com>, Andrew Lunn <andrew@lunn.ch>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Gross <agross@kernel.org>, Andy Lutomirski <luto@kernel.org>,
Andy Shevchenko <andy@infradead.org>,
Anup Patel <anup.patel@wdc.com>, Ard Biesheuvel <ardb@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Christoph Hellwig <hch@lst.de>, Christoph Lameter <cl@linux.com>,
Daniel Vetter <daniel@ffwll.ch>,
Dave Hansen <dave.hansen@linux.intel.com>,
David Airlie <airlied@linux.ie>,
David Laight <David.Laight@aculab.com>,
Dennis Zhou <dennis@kernel.org>,
Dinh Nguyen <dinguyen@kernel.org>,
Geetha sowjanya <gakula@marvell.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Guo Ren <guoren@kernel.org>, Hans de Goede <hdegoede@redhat.com>,
Heiko Carstens <hca@linux.ibm.com>,
Ian Rogers <irogers@google.com>, Ingo Molnar <mingo@redhat.com>,
Jakub Kicinski <kuba@kernel.org>,
Jason Wessel <jason.wessel@windriver.com>,
Jens Axboe <axboe@fb.com>, Jiri Olsa <jolsa@redhat.com>,
Jonathan Cameron <jic23@kernel.org>,
Juri Lelli <juri.lelli@redhat.com>,
Kalle Valo <kvalo@codeaurora.org>,
Kees Cook <keescook@chromium.org>,
Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
Lee Jones <lee.jones@linaro.org>, Marc Zyngier <maz@kernel.org>,
Marcin Wojtas <mw@semihalf.com>,
Mark Gross <markgross@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Matti Vaittinen <mazziesaccount@gmail.com>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Mel Gorman <mgorman@suse.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>,
Nicholas Piggin <npiggin@gmail.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Peter Zijlstra <peterz@infradead.org>,
Petr Mladek <pmladek@suse.com>,
Randy Dunlap <rdunlap@infradead.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Roy Pledge <Roy.Pledge@nxp.com>,
Russell King <linux@armlinux.org.uk>,
Saeed Mahameed <saeedm@nvidia.com>,
Sagi Grimberg <sagi@grimberg.me>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Solomon Peachy <pizza@shaftnet.org>,
Stephen Boyd <sboyd@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Steven Rostedt <rostedt@goodmis.org>,
Subbaraya Sundeep <sbhatta@marvell.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Sunil Goutham <sgoutham@marvell.com>,
Tariq Toukan <tariqt@nvidia.com>, Tejun Heo <tj@kernel.org>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ulf Hansson <ulf.hansson@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Vineet Gupta <vgupta@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Vivien Didelot <vivien.didelot@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>,
bcm-kernel-feedback-list@broadcom.com, kvm@vger.kernel.org,
linux-alpha@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-crypto@vger.kernel.org, linux-csky@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org,
linux-mm@kvack.org, linux-perf-users@vger.kernel.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
linux-snps-arc@lists.infradead.org,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 0/9] lib/bitmap: optimize bitmap_weight() usage
Date: Sun, 28 Nov 2021 19:05:14 +0100 [thread overview]
Message-ID: <YaPEfZ0t9UFGwpml@qmqm.qmqm.pl> (raw)
Message-ID: <20211128180514.nepaRaB8WjMDQcy9o9_XdZpNhfU0WCdBjPs62W6tRS4@z> (raw)
On Sat, Nov 27, 2021 at 07:56:55PM -0800, Yury Norov wrote:
> In many cases people use bitmap_weight()-based functions like this:
>
> if (num_present_cpus() > 1)
> do_something();
>
> This may take considerable amount of time on many-cpus machines because
> num_present_cpus() will traverse every word of underlying cpumask
> unconditionally.
>
> We can significantly improve on it for many real cases if stop traversing
> the mask as soon as we count present cpus to any number greater than 1:
>
> if (num_present_cpus_gt(1))
> do_something();
>
> To implement this idea, the series adds bitmap_weight_{eq,gt,le}
> functions together with corresponding wrappers in cpumask and nodemask.
Having slept on it I have more structured thoughts:
First, I like substituting bitmap_empty/full where possible - I think
the change stands on its own, so could be split and sent as is.
I don't like the proposed API very much. One problem is that it hides
the comparison operator and makes call sites less readable:
bitmap_weight(...) > N
becomes:
bitmap_weight_gt(..., N)
and:
bitmap_weight(...) <= N
becomes:
bitmap_weight_lt(..., N+1)
or:
!bitmap_weight_gt(..., N)
I'd rather see something resembling memcmp() API that's known enough
to be easier to grasp. For above examples:
bitmap_weight_cmp(..., N) > 0
bitmap_weight_cmp(..., N) <= 0
...
This would also make the implementation easier in not having to
copy and paste the code three times. Could also use a simple
optimization reducing code size:
#include <linux/overflow.h>
int bitmap_weight_cmp(long *bits, size_t nbits, size_t cmp)
{
for (size_t i = 0; i < nbits / BITS_PER_LONG; ++i, ++bits)
if (check_sub_overflow(cmp, popcount(*bits), &cmp))
return 1;
nbits %= BITS_PER_LONG;
if (nbits && check_sub_overflow(cmp,
popcount(*bits & GENMASK(nbits)), &cmp))
return 1;
return cmp ? -1 : 0;
}
Best Regards
Michał Mirosław
next prev reply other threads:[~2021-11-28 18:07 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-28 3:56 [PATCH 0/9] lib/bitmap: optimize bitmap_weight() usage Yury Norov
2021-11-28 3:56 ` [PATCH 1/9] lib/bitmap: add bitmap_weight_{eq,gt,le} Yury Norov
2021-11-28 3:56 ` [PATCH 2/9] lib/bitmap: implement bitmap_{empty,full} with bitmap_weight_eq() Yury Norov
2021-11-28 4:37 ` Michał Mirosław
2021-11-28 6:27 ` Yury Norov
2021-11-28 18:10 ` Michał Mirosław
2021-12-14 19:43 ` Yury Norov
2021-12-15 8:40 ` David Laight
2021-12-15 17:45 ` Yury Norov
2021-11-28 3:56 ` [PATCH 3/9] all: replace bitmap_weigth() with bitmap_{empty,full,eq,gt,le} Yury Norov
2021-11-28 4:47 ` Michał Mirosław
2021-11-28 8:01 ` Greg Kroah-Hartman
2021-11-28 3:56 ` [PATCH 4/9] tools: sync bitmap_weight() usage with the kernel Yury Norov
2021-11-28 3:57 ` [PATCH 5/9] lib/cpumask: add cpumask_weight_{eq,gt,le} Yury Norov
2021-11-28 3:57 ` [PATCH 6/9] lib/nodemask: add nodemask_weight_{eq,gt,le} Yury Norov
2021-11-28 3:57 ` [PATCH 7/9] lib/cpumask: add num_{possible,present,active}_cpus_{eq,gt,le} Yury Norov
2021-11-28 4:56 ` Michał Mirosław
2021-11-28 5:09 ` Michał Mirosław
2021-11-28 6:34 ` Yury Norov
2021-11-28 17:07 ` Joe Perches
2021-11-28 17:43 ` Yury Norov
2021-11-28 17:54 ` Dennis Zhou
2021-11-28 18:47 ` Yury Norov
2021-11-28 17:56 ` Emil Renner Berthing
2021-11-28 17:57 ` Joe Perches
2021-11-28 3:57 ` [PATCH 8/9] lib/nodemask: add num_node_state_eq() Yury Norov
2021-11-28 3:57 ` [PATCH 9/9] MAINTAINERS: add cpumask and nodemask files to BITMAP_API Yury Norov
2021-11-28 11:08 ` [PATCH 0/9] lib/bitmap: optimize bitmap_weight() usage Nicholas Piggin
2021-11-28 23:36 ` Yury Norov
2021-11-28 18:03 ` mirq-test [this message]
2021-11-28 18:05 ` Michał Mirosław
2021-11-29 6:38 ` Yury Norov
2021-11-29 16:34 ` Michał Mirosław
2021-12-02 0:31 ` Yury Norov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YaPEfZ0t9UFGwpml@qmqm.qmqm.pl \
--to=mirq-linux@rere.qmqm.pl \
--cc=David.Laight@aculab.com \
--cc=Roy.Pledge@nxp.com \
--cc=acme@kernel.org \
--cc=agross@kernel.org \
--cc=airlied@linux.ie \
--cc=ak@linux.intel.com \
--cc=aklimov@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=amitkarwar@gmail.com \
--cc=andrew@lunn.ch \
--cc=andy@infradead.org \
--cc=anup.patel@wdc.com \
--cc=ardb@kernel.org \
--cc=arnd@arndb.de \
--cc=axboe@fb.com \
--cc=bcm-kernel-feedback-list@broadcom.com \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=cl@linux.com \
--cc=daniel@ffwll.ch \
--cc=dave.hansen@linux.intel.com \
--cc=dennis@kernel.org \
--cc=dinguyen@kernel.org \
--cc=gakula@marvell.com \
--cc=geert@linux-m68k.org \
--cc=gregkh@linuxfoundation.org \
--cc=guoren@kernel.org \
--cc=hca@linux.ibm.com \
--cc=hch@lst.de \
--cc=hdegoede@redhat.com \
--cc=irogers@google.com \
--cc=jason.wessel@windriver.com \
--cc=jejb@linux.ibm.com \
--cc=jic23@kernel.org \
--cc=jolsa@redhat.com \
--cc=juri.lelli@redhat.com \
--cc=keescook@chromium.org \
--cc=krzysztof.kozlowski@canonical.com \
--cc=kuba@kernel.org \
--cc=kvalo@codeaurora.org \
--cc=kvm@vger.kernel.org \
--cc=lee.jones@linaro.org \
--cc=linux-alpha@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-crypto@vger.kernel.org \
--cc=linux-csky@vger.kernel.org \
--cc=linux-ia64@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux-snps-arc@lists.infradead.org \
--cc=linux@armlinux.org.uk \
--cc=linux@rasmusvillemoes.dk \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=luto@kernel.org \
--cc=mark.rutland@arm.com \
--cc=markgross@kernel.org \
--cc=martin.petersen@oracle.com \
--cc=maz@kernel.org \
--cc=mazziesaccount@gmail.com \
--cc=mchehab@kernel.org \
--cc=mgorman@suse.de \
--cc=mike.marciniszyn@cornelisnetworks.com \
--cc=mingo@redhat.com \
--cc=mpe@ellerman.id.au \
--cc=mw@semihalf.com \
--cc=npiggin@gmail.com \
--cc=palmer@dabbelt.com \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=pizza@shaftnet.org \
--cc=pmladek@suse.com \
--cc=rafael@kernel.org \
--cc=rdunlap@infradead.org \
--cc=rostedt@goodmis.org \
--cc=saeedm@nvidia.com \
--cc=sagi@grimberg.me \
--cc=sbhatta@marvell.com \
--cc=sboyd@kernel.org \
--cc=senozhatsky@chromium.org \
--cc=sfr@canb.auug.org.au \
--cc=sgoutham@marvell.com \
--cc=sudeep.holla@arm.com \
--cc=tariqt@nvidia.com \
--cc=tglx@linutronix.de \
--cc=tj@kernel.org \
--cc=tsbogend@alpha.franken.de \
--cc=ulf.hansson@linaro.org \
--cc=vbabka@suse.cz \
--cc=vgupta@kernel.org \
--cc=vincent.guittot@linaro.org \
--cc=viresh.kumar@linaro.org \
--cc=vivien.didelot@gmail.com \
--cc=will@kernel.org \
--cc=yury.norov@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).