From: Yury Norov <yury.norov@gmail.com>
To: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
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
Subject: Re: [PATCH 7/9] lib/cpumask: add num_{possible,present,active}_cpus_{eq,gt,le}
Date: Sat, 27 Nov 2021 22:34:47 -0800 [thread overview]
Message-ID: <20211128063447.GA270945@lapt> (raw)
In-Reply-To: <YaMME60Jfiz5BeJF@qmqm.qmqm.pl>
(restore CC list)
On Sun, Nov 28, 2021 at 05:56:51AM +0100, Michał Mirosław wrote:
> On Sat, Nov 27, 2021 at 07:57:02PM -0800, Yury Norov wrote:
> > Add num_{possible,present,active}_cpus_{eq,gt,le} and replace num_*_cpus()
> > with one of new functions where appropriate. This allows num_*_cpus_*()
> > to return earlier depending on the condition.
> [...]
> > @@ -3193,7 +3193,7 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
> >
> > /* allocate pages */
> > j = 0;
> > - for (unit = 0; unit < num_possible_cpus(); unit++) {
> > + for (unit = 0; num_possible_cpus_gt(unit); unit++) {
>
> This looks dubious.
Only this?
> The old version I could hope the compiler would call
> num_possible_cpus() only once if it's marked const or pure, but the
> alternative is going to count the bits every time making this a guaranteed
> O(n^2) even though the bitmap doesn't change.
num_possible_cpus() is not const neither pure. This is O(n^2) before and after.
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next prev parent reply other threads:[~2021-11-28 6:34 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211128035704.270739-1-yury.norov@gmail.com>
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 3:56 ` [PATCH 3/9] all: replace bitmap_weigth() with bitmap_{empty,full,eq,gt,le} Yury Norov
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 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
[not found] ` <20211128035704.270739-4-yury.norov@gmail.com>
2021-11-28 4:47 ` [PATCH 3/9] all: replace bitmap_weigth() with bitmap_{empty,full,eq,gt,le} Michał Mirosław
2021-11-28 8:01 ` Greg Kroah-Hartman
[not found] ` <20211128035704.270739-8-yury.norov@gmail.com>
2021-11-28 4:56 ` [PATCH 7/9] lib/cpumask: add num_{possible,present,active}_cpus_{eq,gt,le} Michał Mirosław
2021-11-28 5:09 ` Michał Mirosław
2021-11-28 6:34 ` Yury Norov [this message]
2021-11-28 17:07 ` Joe Perches
[not found] ` <8f389151c39a8a5b6b31d5238cb680305225d9f2.camel@perches.com>
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 11:08 ` [PATCH 0/9] lib/bitmap: optimize bitmap_weight() usage Nicholas Piggin
2021-11-28 18:03 ` mirq-test
2021-11-29 6:38 ` Yury Norov
2021-11-29 16:34 ` Michał Mirosław
2021-12-02 0:31 ` Yury Norov
[not found] ` <20211128035704.270739-3-yury.norov@gmail.com>
2021-11-28 4:37 ` [PATCH 2/9] lib/bitmap: implement bitmap_{empty,full} with bitmap_weight_eq() 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
[not found] ` <1638096766.3elxdzb8ly.astroid@bobo.none>
2021-11-28 23:36 ` [PATCH 0/9] lib/bitmap: optimize bitmap_weight() usage Yury Norov
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