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Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/wr
From: |
Peter Lieven |
Subject: |
Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests |
Date: |
Mon, 8 Sep 2014 18:18:26 +0200 |
> Am 08.09.2014 um 17:27 schrieb Paolo Bonzini <address@hidden>:
>
> 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.
>
>
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, (continued)
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, ronnie sahlberg, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests,
Peter Lieven <=
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/08
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/12
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/18
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/18
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Paolo Bonzini, 2014/09/18
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/18
- Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests, Peter Lieven, 2014/09/08
[Qemu-devel] [PATCH 3/4] block/iscsi: set max_transfer_length, Peter Lieven, 2014/09/05
[Qemu-devel] [PATCH 4/4] block: avoid creating oversized writes in multiwrite_merge, Peter Lieven, 2014/09/05