From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Venkatesh Pallipadi <venki@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Mike Travis <travis@sgi.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
Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v4
Date: Thu, 26 Jan 2012 22:52:57 +0530 [thread overview]
Message-ID: <4F218BF1.6050303@linux.vnet.ibm.com> (raw)
In-Reply-To: <1327447541-3040-1-git-send-email-venki@google.com>
On 01/25/2012 04:55 AM, Venkatesh Pallipadi 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.
>
> Signed-off-by: Venkatesh Pallipadi <venki@google.com>
> ---
Looks good to me now :-)
Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Regards,
Srivatsa S. Bhat
next prev parent reply other threads:[~2012-01-26 17:23 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 [this message]
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
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
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