linux-kernel - Re: [PATCH] sched: minor optimizations in wake_affine and select_task_rq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20080930070158.GA12465@elte.hu>
Date:	Tue, 30 Sep 2008 09:01:58 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, vatsa@...ux.vnet.ibm.com,
	a.p.zijlstra@...llo.nl
Subject: Re: [PATCH] sched: minor optimizations in wake_affine and
	select_task_rq_fair


* Chris Friesen <cfriesen@...tel.com> wrote:

> Amit K. Arora wrote:
>> Hello,
>>
>> Please consider this patch. It makes a few minor changes to
>> sched_fair.c.
>>
>>
>> sched: Minor optimizations in wake_affine and select_task_rq_fair
>>
>> This patch does following:
>> o Reduces the number of arguments to wake_affine().
>
> At what point is it cheaper to pass items as args rather than 
> recalculating them?  If reducing the number of args is desirable, what 
> about removing the "this_cpu" and "prev_cpu" args and recalculating 
> them in wake_affine()?

it's usually not worth it, especially if it leads to duplicated 
calculations (and code) like:

+       unsigned int imbalance = 100 + (this_sd->imbalance_pct - 100) / 2;

gcc will optimize it away because it's all static functions, but still.

'size kernel/sched.o' should be a good guideline: if the .o's text 
section gets smaller due to a patch it usually gets faster as well.

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/