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From: Peter Lieven <pl@kamp.de>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Benoît Canet" <benoit.canet@irqsave.net>,
	"Kevin Wolf" <kwolf@redhat.com>,
	"ronnie sahlberg" <ronniesahlberg@gmail.com>,
	qemu-devel <qemu-devel@nongnu.org>,
	"Max Reitz" <mreitz@redhat.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests
Date: Mon, 8 Sep 2014 18:18:26 +0200	[thread overview]
Message-ID: <29A6ECA0-C6CE-4557-80CA-31FD2CA199A2@kamp.de> (raw)
In-Reply-To: <540DCAE8.4060701@redhat.com>



> Am 08.09.2014 um 17:27 schrieb Paolo Bonzini <pbonzini@redhat.com>:
> 
> Il 08/09/2014 17:18, Peter Lieven ha scritto:
>>> 
>>> That's why we have splitting code for discard, and why we would have to
>>> add it for read/write too.
>> 
>> Why should a guest generate such big requests.
> 
> When copying data, gparted will try using very large I/O sizes.  Of
> course if something breaks it will just use a smaller size, but it would
> make performance worse.
> 
> I tried now (with local storage, not virtual---but with such large block
> sizes it's disk bound anyway, one request can take 0.1 seconds to
> execute) and a 2 MB block size is 20% slower than 16 MB block size on
> your usual 3.5" rotational SATA disk.
> 

can you share with what command exactly you ran these tests?

i tried myself and found that without multiwrite_merge i was not able to create a request bigger than 0xffff sectors from inside linux.

Peter

> Paolo
> 
>> Afaik the reported
>> limit for e.g. virtio-blk is 1024 sectors (reported through blockdev
>> --getmaxsect /dev/vda).
>> I think it was only the multiwrite_merge code causing trouble here.
> 
> 

  reply	other threads:[~2014-09-08 16:18 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-05 16:51 [Qemu-devel] [PATCH 0/4] introduce max_transfer_length Peter Lieven
2014-09-05 16:51 ` [Qemu-devel] [PATCH 1/4] BlockLimits: " Peter Lieven
2014-09-05 16:51 ` [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests Peter Lieven
2014-09-08 13:44   ` Benoît Canet
2014-09-08 13:49     ` Paolo Bonzini
2014-09-08 13:56       ` Peter Lieven
2014-09-08 13:58         ` Paolo Bonzini
2014-09-08 14:35           ` Peter Lieven
2014-09-08 14:42             ` Paolo Bonzini
2014-09-08 14:54               ` Peter Lieven
2014-09-23  8:47                 ` Kevin Wolf
2014-09-23  8:55                   ` Peter Lieven
2014-09-23  9:09                     ` Kevin Wolf
2014-09-08 15:13               ` ronnie sahlberg
2014-09-08 15:15                 ` Paolo Bonzini
2014-09-08 15:18                   ` Peter Lieven
2014-09-08 15:27                     ` Paolo Bonzini
2014-09-08 16:18                       ` Peter Lieven [this message]
2014-09-08 16:29                         ` Paolo Bonzini
2014-09-12 11:43                           ` Peter Lieven
2014-09-18 14:12                             ` Paolo Bonzini
2014-09-18 14:16                               ` Peter Lieven
2014-09-18 14:17                                 ` Paolo Bonzini
2014-09-18 22:57                                   ` Peter Lieven
2014-09-08 15:16                 ` Peter Lieven
2014-09-05 16:51 ` [Qemu-devel] [PATCH 3/4] block/iscsi: set max_transfer_length Peter Lieven
2014-09-05 16:51 ` [Qemu-devel] [PATCH 4/4] block: avoid creating oversized writes in multiwrite_merge Peter Lieven
2014-09-18 14:13   ` Paolo Bonzini
2014-09-18 22:56     ` Peter Lieven
2014-09-19 13:33       ` Paolo Bonzini
2014-09-22  9:43         ` Peter Lieven
2014-09-22 19:06           ` Paolo Bonzini
2014-09-23  6:15             ` Peter Lieven
2014-09-23  8:59               ` Kevin Wolf
2014-09-23  9:04                 ` Peter Lieven
2014-09-23  9:32                 ` Peter Lieven
2014-09-23  9:47                   ` Kevin Wolf
2014-09-23  9:52                     ` Peter Lieven
2014-09-23 10:05                       ` Kevin Wolf
2014-09-30  7:26                         ` Peter Lieven
2014-09-30  8:03                           ` Kevin Wolf
2014-09-05 17:05 ` [Qemu-devel] [PATCH 0/4] introduce max_transfer_length ronnie sahlberg
2014-09-05 19:52   ` Peter Lieven
2014-09-05 21:22     ` ronnie sahlberg

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