linux-kernel - Re: [PATCH] cfq-iosched: rework seeky detection

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: <4B4A92C7.10303@cn.fujitsu.com>
Date:	Mon, 11 Jan 2010 10:53:59 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Shaohua Li <shaohua.li@...el.com>,
	Corrado Zoccolo <czoccolo@...il.com>
CC:	Jens Axboe <jens.axboe@...cle.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jeff Moyer <jmoyer@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH] cfq-iosched: rework seeky detection

Shaohua Li wrote:
> On Sat, Jan 09, 2010 at 11:59:17PM +0800, Corrado Zoccolo wrote:
>> Current seeky detection is based on average seek lenght.
>> This is suboptimal, since the average will not distinguish between:
>> * a process doing medium sized seeks
>> * a process doing some sequential requests interleaved with larger seeks
>> and even a medium seek can take lot of time, if the requested sector
>> happens to be behind the disk head in the rotation (50% probability).
>>
>> Therefore, we change the seeky queue detection to work as follows:
>> * each request can be classified as sequential if it is very close to
>>   the current head position, i.e. it is likely in the disk cache (disks
>>   usually read more data than requested, and put it in cache for
>>   subsequent reads). Otherwise, the request is classified as seeky.
>> * an history window of the last 32 requests is kept, storing the
>>   classification result.
>> * A queue is marked as seeky if more than 1/8 of the last 32 requests
>>   were seeky.
>>
>> This patch fixes a regression reported by Yanmin, on mmap 64k random
>> reads.
> Can we not count a big request (say the request data is >= 32k) as seeky
> regardless the seek distance? In this way we can also make a 64k random sync
> read not as seeky.

  Or maybe we can rely on *dynamic* CFQQ_SEEK_THR in terms of data lenght to 
  determine whether a request should be a seeky one.

> 
> Thanks,
> Shaohua
> 
> 
> 

-- 
Regards
Gui Jianfeng

--
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/