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Re: [Qemu-devel] qemu-img convert cache mode for source
From: |
Peter Lieven |
Subject: |
Re: [Qemu-devel] qemu-img convert cache mode for source |
Date: |
Wed, 05 Mar 2014 15:44:17 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 |
Am 04.03.2014 10:24, schrieb Stefan Hajnoczi:
> On Mon, Mar 03, 2014 at 01:20:21PM +0100, Peter Lieven wrote:
>> On 03.03.2014 13:03, Stefan Hajnoczi wrote:
>>> So what is the actual performance problem you are trying to solve and
>>> what benchmark output are you getting when you compare with
>>> FADV_DONTNEED against without FADV_DONTNEED?
>> I found the performance to be identical. For the problem see below please.
>>> I think there's a danger that the discussion will go around in circles.
>>> Please post the performance results that kicked off this whole effort
>>> and let's focus on the data. That way it's much easier to evaluate what
>>> changes to QEMU are a win and which are not necessary.
>> I found that under memory pressure situations the increasing buffers
>> leads to vserver memory being swapped out. This caused trouble
>> especially in overcommit scenarios (where all memory is backed by
>> swap).
> I think the general idea is qemu-img should not impact running guests,
> even on a heavily loaded machine. But again, this needs to be discussed
> using concrete benchmarks with configurations and results posted to the
> list.
Sure, this is why I started to look at this. I found that under high memory
pressure a backup (local storage -> NFS) causes swapping. I started to
use libnfs as destination to avoid influence of the kernel NFS client. But
I saw that the buffers still increase while a backup is running. With the
proposed patch I sent recently
[PATCH] block: introduce BDRV_O_SEQUENTIAL
I don't see this behaviour while I have not yet observed a performance penalty.
Peter
>
> Stefan
- Re: [Qemu-devel] qemu-img convert cache mode for source, Kevin Wolf, 2014/03/03
- Re: [Qemu-devel] qemu-img convert cache mode for source, Kevin Wolf, 2014/03/03
- Re: [Qemu-devel] qemu-img convert cache mode for source, Stefan Hajnoczi, 2014/03/03
- Re: [Qemu-devel] qemu-img convert cache mode for source, Peter Lieven, 2014/03/03
- Re: [Qemu-devel] qemu-img convert cache mode for source, Stefan Hajnoczi, 2014/03/04
- Re: [Qemu-devel] qemu-img convert cache mode for source,
Peter Lieven <=
- Re: [Qemu-devel] qemu-img convert cache mode for source, Marcus, 2014/03/05
- Re: [Qemu-devel] qemu-img convert cache mode for source, Peter Lieven, 2014/03/05
- Re: [Qemu-devel] qemu-img convert cache mode for source, Marcus, 2014/03/05
- Re: [Qemu-devel] qemu-img convert cache mode for source, Peter Lieven, 2014/03/05
- Re: [Qemu-devel] qemu-img convert cache mode for source, Stefan Hajnoczi, 2014/03/06
- Re: [Qemu-devel] qemu-img convert cache mode for source, Peter Lieven, 2014/03/06
- Re: [Qemu-devel] qemu-img convert cache mode for source, Stefan Hajnoczi, 2014/03/06
- Re: [Qemu-devel] qemu-img convert cache mode for source, Paolo Bonzini, 2014/03/06
- Re: [Qemu-devel] qemu-img convert cache mode for source, Liguori, Anthony, 2014/03/06
- Re: [Qemu-devel] qemu-img convert cache mode for source, Peter Lieven, 2014/03/06