From: Andrew Morton <akpm@linux-foundation.org>
To: Venkatesh Pallipadi <venki@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Mike Travis <travis@sgi.com>,
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
"Paul E. McKenney" <paul.mckenney@linaro.org>,
"Rafael J. Wysocki" <rjw@sisk.pl>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
linux-kernel@vger.kernel.org,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5
Date: Wed, 1 Feb 2012 14:01:25 -0800 [thread overview]
Message-ID: <20120201140125.c656df41.akpm@linux-foundation.org> (raw)
In-Reply-To: <1328055439-9441-1-git-send-email-venki@google.com>
On Tue, 31 Jan 2012 16:17:19 -0800
Venkatesh Pallipadi <venki@google.com> wrote:
> Kernel's notion of possible cpus (from include/linux/cpumask.h)
> * cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
>
> * The cpu_possible_mask is fixed at boot time, as the set of CPU id's
> * that it is possible might ever be plugged in at anytime during the
> * life of that system boot.
>
> #define num_possible_cpus() cpumask_weight(cpu_possible_mask)
>
> and on x86 cpumask_weight() calls hweight64 and hweight64 (on older kernels
> and systems with !X86_FEATURE_POPCNT) or a popcnt based alternative.
>
> i.e, We needlessly go through this mask based calculation everytime
> num_possible_cpus() is called.
>
> The problem is there with cpu_online_mask() as well, which is fixed value at
> boot time in !CONFIG_HOTPLUG_CPU case and should not change that often even
> in HOTPLUG case.
>
> Though most of the callers of these two routines are init time (with few
> exceptions of runtime calls), it is cleaner to use variables
> and not go through this repeated mask based calculation.
Looks good to me.
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -604,9 +604,13 @@ EXPORT_SYMBOL(cpu_all_bits);
> #ifdef CONFIG_INIT_ALL_POSSIBLE
> static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
> = CPU_BITS_ALL;
> +unsigned int nr_possible_cpus __read_mostly = CONFIG_NR_CPUS;
> #else
> static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
> +unsigned int nr_possible_cpus __read_mostly;
> #endif
> +EXPORT_SYMBOL(nr_possible_cpus);
What the heck is CONFIG_INIT_ALL_POSSIBLE?
<blames Rusty>
: 1) Some archs (m32, parisc, s390) set possible_map to all 1, so we add a
: CONFIG_INIT_ALL_POSSIBLE for this rather than break them.
Seems strange. Do these architectures really need to initialise
cpu_possible_map at compile-time, when all the other architectures
manage to do it at runtime?
next prev parent reply other threads:[~2012-02-01 22:01 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-18 2:07 [PATCH] Avoid mask based num_possible_cpus and num_online_cpus Venkatesh Pallipadi
2012-01-18 5:55 ` KOSAKI Motohiro
2012-01-18 18:52 ` Venki Pallipadi
2012-01-18 19:20 ` KOSAKI Motohiro
2012-01-19 20:01 ` Venkatesh Pallipadi
2012-01-19 20:40 ` KOSAKI Motohiro
2012-01-21 1:01 ` Venki Pallipadi
2012-01-19 20:43 ` Srivatsa S. Bhat
2012-01-20 23:09 ` Venki Pallipadi
2012-01-20 23:45 ` KOSAKI Motohiro
2012-01-20 23:55 ` Venki Pallipadi
2012-01-23 5:22 ` Srivatsa S. Bhat
2012-01-23 19:28 ` Venki Pallipadi
2012-01-24 2:34 ` [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v3 Venkatesh Pallipadi
2012-01-24 19:22 ` Srivatsa S. Bhat
2012-01-24 19:30 ` KOSAKI Motohiro
2012-01-24 21:01 ` Venki Pallipadi
2012-01-24 23:25 ` [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v4 Venkatesh Pallipadi
2012-01-26 17:22 ` Srivatsa S. Bhat
2012-01-26 17:27 ` Srivatsa S. Bhat
2012-01-26 21:25 ` KOSAKI Motohiro
2012-01-26 23:22 ` Andrew Morton
2012-01-27 23:58 ` Venki Pallipadi
2012-02-01 0:17 ` [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 Venkatesh Pallipadi
2012-02-01 22:01 ` Andrew Morton [this message]
2012-02-02 20:03 ` Rusty Russell
2012-02-02 20:19 ` Andrew Morton
2012-02-02 21:00 ` Venki Pallipadi
2012-02-13 19:54 ` Tony Luck
2012-02-13 20:04 ` Venki Pallipadi
2012-02-13 20:25 ` Srivatsa S. Bhat
2012-02-13 20:43 ` Venki Pallipadi
2012-02-13 20:55 ` Srivatsa S. Bhat
2012-02-13 20:44 ` Srivatsa S. Bhat
2012-02-13 21:57 ` Tony Luck
2012-02-14 9:25 ` Rusty Russell
2012-02-14 21:35 ` Srivatsa S. Bhat
2012-02-14 23:00 ` Tony Luck
2012-02-14 22:49 ` [PATCH 0/3] Cleanup raw handling of online/possible map Venkatesh Pallipadi
2012-02-14 22:49 ` [PATCH 1/3] hexagon: Avoid raw handling of cpu_possible_map Venkatesh Pallipadi
2012-02-14 22:49 ` [PATCH 2/3] mips: Avoid raw handling of cpu_possible_map/cpu_online_map Venkatesh Pallipadi
2012-02-27 22:19 ` David Daney
2012-02-14 22:49 ` [PATCH 3/3] um: Avoid raw handling of cpu_online_map Venkatesh Pallipadi
2012-02-27 21:55 ` [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 David Daney
2012-02-27 22:07 ` Andrew Morton
2012-02-27 22:16 ` David Daney
2012-03-01 18:32 ` Venki Pallipadi
2012-02-28 5:01 ` Stephen Rothwell
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=20120201140125.c656df41.akpm@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=kosaki.motohiro@gmail.com \
--cc=kosaki.motohiro@jp.fujitsu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=paul.gortmaker@windriver.com \
--cc=paul.mckenney@linaro.org \
--cc=rjw@sisk.pl \
--cc=rusty@rustcorp.com.au \
--cc=srivatsa.bhat@linux.vnet.ibm.com \
--cc=travis@sgi.com \
--cc=venki@google.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 NNTP newsgroup(s).