From: Nick Piggin <piggin@cyberone.com.au>
To: Andrea Arcangeli <andrea@suse.de>
Cc: Jakob Oestergaard <jakob@unthought.net>,
Andrew Morton <akpm@digeo.com>,
David Lang <david.lang@digitalinsight.com>,
riel@conectiva.com.br, ckolivas@yahoo.com.au,
linux-kernel@vger.kernel.org, axboe@suse.de
Subject: Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]
Date: Mon, 10 Feb 2003 19:27:51 +1100 [thread overview]
Message-ID: <3E476287.8070407@cyberone.com.au> (raw)
In-Reply-To: 20030210080858.GM31401@dualathlon.random
Andrea Arcangeli wrote:
>On Mon, Feb 10, 2003 at 06:41:14PM +1100, Nick Piggin wrote:
>
>>Andrea Arcangeli wrote:
>>
>>
>>>On Mon, Feb 10, 2003 at 03:58:26PM +1100, Nick Piggin wrote:
>>>
>>>>Remember that readahead gets scaled down quickly if it isn't
>>>>getting hits. It is also likely to be sequential and in the
>>>>track buffer, so it is a small cost.
>>>>
>>>>Huge readahead is a problem however anticipatory scheduling
>>>>will hopefully allow good throughput for multiple read streams
>>>>without requiring much readahead.
>>>>
What I mean by this is: if we have >1 sequential readers (eg. ftp
server), lets say 30MB/s disk, 4ms avg seek+settle+blah time,
submitting reads in say 128KB chunks alternating between streams
will cut throughput in half... At 1MB readahead we're at 89%
throughput. At 2MB, 94%
With anticipatory scheduling, we can give each stream say 100ms
so thats 96% with, say... 8K readahead if you like. (Yes, I am
aware that CPU/PCI/IDE efficiency also mandates a larger request
size).
Anyway that is the theory. It remains to be seen if we can make
it work.
>>>>
>>>>
>>>the main purpose of readahead is to generate 512k scsi commands when you
>>>read a file with a 4k user buffer, anticipatory scheduling isn't very
>>>related to readahead.
>>>
>>>
>>You seem to be forgetting things like seek time.
>>
>
>I didn't say it's the only purpose. Of course there's no hope for
>merging in the metadata dependent reads of the fs where anticipatory
>scheduling does its best, and infact they don't even attempt to do any
>readhaead. BTW, one thing that should definitely do readhaead and it's
>not doing that (at least in 2.4) is the readdir path, again to generate
>big commands, no matter the seeks. It was lost with the directory in
>pagecache.
>
>Andrea
>
>
>
>
next prev parent reply other threads:[~2003-02-10 8:18 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-02-09 13:30 [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest Con Kolivas
2003-02-09 14:46 ` stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest] Andrea Arcangeli
2003-02-10 3:13 ` Nick Piggin
2003-02-10 3:52 ` Rik van Riel
2003-02-10 4:44 ` Nick Piggin
2003-02-10 5:15 ` usbaudio.c 2.5.59 John
2003-02-10 7:26 ` stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest] Andrea Arcangeli
2003-02-10 7:43 ` Nick Piggin
2003-02-10 3:42 ` Rik van Riel
2003-02-10 4:15 ` Rik van Riel
2003-02-10 4:19 ` David Lang
2003-02-10 4:29 ` Rik van Riel
2003-02-10 7:20 ` Andrea Arcangeli
2003-02-10 4:33 ` Andrew Morton
2003-02-10 4:47 ` Rik van Riel
2003-02-10 7:31 ` Andrea Arcangeli
2003-02-10 4:51 ` Jakob Oestergaard
2003-02-10 4:58 ` Nick Piggin
2003-02-10 5:10 ` Jakob Oestergaard
2003-02-10 6:06 ` Valdis.Kletnieks
2003-02-10 6:31 ` Jakob Oestergaard
2003-02-10 7:36 ` Andrea Arcangeli
2003-02-10 7:41 ` Nick Piggin
2003-02-10 8:08 ` Andrea Arcangeli
2003-02-10 8:19 ` Andrew Morton
2003-02-10 8:56 ` Andrea Arcangeli
2003-02-10 9:09 ` Andrew Morton
2003-02-10 9:14 ` Andrea Arcangeli
2003-02-10 10:07 ` Hans Reiser
2003-02-10 10:15 ` Andrea Arcangeli
2003-02-10 10:40 ` Nick Piggin
2003-02-10 11:10 ` Andrea Arcangeli
2003-02-10 11:21 ` Andrew Morton
2003-02-10 11:31 ` Andrea Arcangeli
2003-02-10 11:24 ` Nick Piggin
2003-02-10 11:39 ` Andrea Arcangeli
2003-02-10 11:45 ` Nick Piggin
2003-02-10 12:00 ` Andrea Arcangeli
2003-02-10 12:11 ` Nick Piggin
2003-02-10 12:22 ` Andrea Arcangeli
2003-02-10 12:36 ` Nick Piggin
2003-02-10 12:47 ` Andrea Arcangeli
2003-02-10 13:26 ` Rik van Riel
2003-02-10 11:48 ` Andrew Morton
2003-02-10 11:53 ` Nick Piggin
2003-02-10 12:10 ` Andrea Arcangeli
2003-02-10 12:14 ` Nick Piggin
2003-02-10 12:26 ` Andrea Arcangeli
2003-02-10 12:12 ` Andrew Morton
2003-02-10 12:25 ` Andrea Arcangeli
2003-02-10 12:27 ` Nick Piggin
2003-02-10 12:30 ` Andrea Arcangeli
2003-02-10 12:34 ` Nick Piggin
2003-02-10 12:43 ` Andrea Arcangeli
2003-02-10 12:55 ` Nick Piggin
2003-02-10 13:30 ` Rik van Riel
2003-02-11 19:13 ` Rod Van Meter
2003-02-10 12:09 ` Andrea Arcangeli
2003-02-10 12:17 ` Nick Piggin
2003-02-10 12:28 ` Andrea Arcangeli
2003-02-10 12:58 ` Hans Reiser
2003-02-10 13:18 ` Andrea Arcangeli
2003-02-10 20:14 ` Hans Reiser
2003-02-10 13:19 ` Nick Piggin
2003-02-10 14:49 ` stochastic fair queueing in the elevator [Re: [BENCHMARK] 2 Giuliano Pochini
2003-02-10 15:05 ` Andrea Arcangeli
2003-02-10 11:25 ` stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest] Hans Reiser
2003-02-10 11:42 ` Andrew Morton
2003-02-10 13:00 ` Hans Reiser
2003-02-10 10:48 ` Andrew Morton
2003-02-10 10:55 ` Nick Piggin
2003-02-10 11:21 ` Andrea Arcangeli
2003-02-10 11:33 ` Andrew Morton
2003-02-10 11:43 ` Andrea Arcangeli
2003-02-10 11:39 ` Nick Piggin
2003-02-10 9:59 ` Hans Reiser
2003-02-10 10:06 ` Andrew Morton
2003-02-10 10:17 ` Hans Reiser
2003-02-10 10:39 ` Hans Reiser
2003-02-10 8:27 ` Nick Piggin [this message]
2003-02-10 9:02 ` Andrea Arcangeli
2003-02-10 9:18 ` Nick Piggin
2003-02-10 20:33 ` Kurt Garloff
2003-02-10 21:43 ` Rik van Riel
2003-02-10 5:01 ` Andrew Morton
2003-02-10 7:34 ` Andrea Arcangeli
2003-02-10 4:44 ` Rik van Riel
2003-02-10 7:31 ` Andrea Arcangeli
2003-02-10 7:17 ` Andrea Arcangeli
2003-02-10 7:39 ` Nick Piggin
2003-02-10 10:03 ` stochastic fair queueing in the elevator [Re: [BENCHMARK] 2 Giuliano Pochini
2003-02-10 16:23 ` stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest] Pavel Machek
2003-02-11 11:49 ` Andrea Arcangeli
2003-02-11 12:43 ` Jens Axboe
2003-02-11 14:28 ` Jason Lunz
2003-02-11 14:41 ` Jens Axboe
2003-02-11 17:17 ` Jason Lunz
2003-02-11 20:19 ` Jens Axboe
2003-02-10 16:47 ` Pavel Machek
2003-02-11 11:01 ` Jens Axboe
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