linux-kernel - Re: Ten percent test

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: <1176172745.6943.58.camel@Homer.simpson.net>
Date:	Tue, 10 Apr 2007 04:39:05 +0200
From:	Mike Galbraith <efault@....de>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Con Kolivas <kernel@...ivas.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	ck list <ck@....kolivas.org>
Subject: Re: Ten percent test

On Mon, 2007-04-09 at 07:38 +0200, Mike Galbraith wrote:

> I don't think you can have very much effect on latency using nice with
> SD once the CPU is fully utilized.  See below.
> 
> /*
>  * This contains a bitmap for each dynamic priority level with empty slots
>  * for the valid priorities each different nice level can have. It allows
>  * us to stagger the slots where differing priorities run in a way that
>  * keeps latency differences between different nice levels at a minimum.
>  * ie, where 0 means a slot for that priority, priority running from left to
>  * right:
>  * nice -20 0000000000000000000000000000000000000000
>  * nice -10 1001000100100010001001000100010010001000
>  * nice   0 0101010101010101010101010101010101010101
>  * nice   5 1101011010110101101011010110101101011011
>  * nice  10 0110111011011101110110111011101101110111
>  * nice  15 0111110111111011111101111101111110111111
>  * nice  19 1111111111111111111011111111111111111111
>  */
> 
> Nice allocates bandwidth, but as long as the CPU is busy, tasks always
> proceed downward in priority until they hit the expired array.  That's
> the design.

There's another aspect of this that may require some thought - kernel
threads.  As load increases, so does rotation length.  Would you really
want CPU hogs routinely preempting house-keepers under load?

	-Mike

-
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/