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From: Chris Mason <mason@suse.com>
To: Andrea Arcangeli <andrea@suse.de>
Cc: Marcelo Tosatti <marcelo@conectiva.com.br>,
	Jens Axboe <axboe@suse.de>, lkml <linux-kernel@vger.kernel.org>,
	"Stephen C. Tweedie" <sct@redhat.com>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Jeff Garzik <jgarzik@pobox.com>, Andrew Morton <akpm@digeo.com>,
	Alexander Viro <viro@math.psu.edu>
Subject: Re: RFC on io-stalls patch
Date: 14 Jul 2003 16:34:41 -0400	[thread overview]
Message-ID: <1058214881.13313.291.camel@tiny.suse.com> (raw)
In-Reply-To: <20030714202434.GS16313@dualathlon.random>

On Mon, 2003-07-14 at 16:24, Andrea Arcangeli wrote:

> 
> this isn't what we had in pre4, this is more equivalent to an hack in
> pre4 where the requests aren't distributed anymore 50/50 but 10/90. Of
> course an I/O queue filled mostly by parallel sync reads, will make the
> writer go slower since it will very rarely find the queue not oversized
> in presence of a flood of readers. So the writer won't be able to make
> progress.
> 
> This is a "stop the writers and give unlimited requests to the reader"
> hack, not a "reserve some request for the reader", of course then the
> reader is faster. of course then, contest shows huge improvements for
> the read loads.

Which is why it's a good place to start.  If we didn't see huge
improvements here, there's no use in experimenting with this tactic
further.

> 
> But contest only benchmarks the reader, it has no clue how fast the
> writer is AFIK. I would love to hear the bandwidth the writer is writing
> into the xtar_load. Maybe it's shown in some of the Loads/LCPU or
> something, but I don't know the semantics of those fields and I only
> look at time and ratio which I understand. so if any contest expert can
> enaborate if the xtar_load bandwidth is taken into consideration
> somewhere I would love to hear.

I had a much longer reply at first as well, but this is only day 1 of
Jens' benchmark, and he had plans to test other workloads.  I'd like to
give him the chance to do that work before we think about merging the
patch.  It's a good starting point for the question "can we do better
for reads?" (clearly the answer is yes).

-chris



  reply	other threads:[~2003-07-14 20:25 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-08 20:06 RFC on io-stalls patch Marcelo Tosatti
2003-07-10 13:57 ` Jens Axboe
2003-07-11 14:13   ` Chris Mason
2003-07-12  0:20     ` Nick Piggin
2003-07-12 18:37       ` Chris Mason
2003-07-12  7:37     ` Jens Axboe
2003-07-12  7:48       ` Jens Axboe
2003-07-12 18:32       ` Chris Mason
2003-07-13  0:33         ` Andrea Arcangeli
2003-07-13  9:01         ` Jens Axboe
2003-07-13 16:20           ` Chris Mason
2003-07-13 16:45             ` Jeff Garzik
2003-07-13 19:33               ` Andrea Arcangeli
2003-07-13 17:47             ` Jens Axboe
2003-07-13 19:35               ` Andrea Arcangeli
2003-07-14  0:36                 ` Chris Mason
2003-07-13 19:19           ` Andrea Arcangeli
2003-07-14  5:49             ` Jens Axboe
2003-07-14 12:23               ` Marcelo Tosatti
2003-07-14 13:12                 ` Jens Axboe
2003-07-14 19:51                   ` Jens Axboe
2003-07-14 20:09                     ` Chris Mason
2003-07-14 20:19                       ` Andrea Arcangeli
2003-07-14 21:24                         ` Chris Mason
2003-07-15  5:46                       ` Jens Axboe
2003-07-14 20:09                     ` Marcelo Tosatti
2003-07-14 20:24                       ` Andrea Arcangeli
2003-07-14 20:34                         ` Chris Mason [this message]
2003-07-15  5:35                           ` Jens Axboe
     [not found]                           ` <20030714224528.GU16313@dualathlon.random>
2003-07-15  5:40                             ` Jens Axboe
     [not found]                             ` <1058229360.13317.364.camel@tiny.suse.com>
2003-07-15  5:43                               ` Jens Axboe
     [not found]                               ` <20030714175238.3eaddd9a.akpm@osdl.org>
     [not found]                                 ` <20030715020706.GC16313@dualathlon.random>
2003-07-15  5:45                                   ` Jens Axboe
2003-07-15  6:01                                     ` Andrea Arcangeli
2003-07-15  6:08                                       ` Jens Axboe
2003-07-15  7:03                                         ` Andrea Arcangeli
2003-07-15  8:28                                           ` Jens Axboe
2003-07-15  9:12                                             ` Chris Mason
2003-07-15  9:17                                               ` Jens Axboe
2003-07-15  9:18                                                 ` Jens Axboe
2003-07-15  9:30                                                   ` Chris Mason
2003-07-15 10:03                                                   ` Andrea Arcangeli
2003-07-15 10:11                                                     ` Jens Axboe
2003-07-15 14:18                                                 ` Chris Mason
2003-07-15 14:29                                                   ` Jens Axboe
2003-07-16 17:06                                                   ` Chris Mason
2003-07-15  9:22                                               ` Chris Mason
2003-07-15  9:59                                               ` Andrea Arcangeli
2003-07-15  9:48                                             ` Andrea Arcangeli
2003-07-14 20:16                     ` Andrea Arcangeli
2003-07-14 20:17                       ` Marcelo Tosatti
2003-07-14 20:27                         ` Andrea Arcangeli
2003-07-15  5:26                       ` Jens Axboe
2003-07-15  5:48                         ` Andrea Arcangeli
2003-07-15  6:01                           ` Jens Axboe
2003-07-15  6:33                             ` Andrea Arcangeli
2003-07-15 11:22                         ` Alan Cox
2003-07-15 11:27                           ` Jens Axboe
2003-07-16 12:43                             ` Andrea Arcangeli
2003-07-16 12:46                               ` Jens Axboe
2003-07-16 12:59                                 ` Andrea Arcangeli
2003-07-16 13:04                                   ` Jens Axboe
2003-07-16 13:11                                     ` Andrea Arcangeli
2003-07-16 13:21                                       ` Jens Axboe
2003-07-16 13:44                                         ` Andrea Arcangeli
2003-07-16 14:00                                           ` Jens Axboe
2003-07-16 14:24                                             ` Andrea Arcangeli
2003-07-16 16:49                                     ` Andrew Morton
2003-07-15 18:47 Shane Shrybman

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