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Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again |
Date: |
Mon, 22 Jun 2009 13:44:35 +0200 |
User-agent: |
Thunderbird 2.0.0.21 (X11/20090320) |
Christoph Hellwig schrieb:
> On Mon, Jun 22, 2009 at 01:18:03PM +0200, Kevin Wolf wrote:
>> Since the patch that suggested it woudl revert qcow2 to writeback caching, in
>> fact none of the drivers has had cache=off as default any more. This patch
>> restores the desired behaviour.
>
> Looks good to me. I still quite hate that BDRV_O_CACHE_DEF thing, just
> makes it too complicated for drivers to get it right.
Actually it's just raw that must get it right. All the other drivers
access their image file through raw.
> Btw, what is the performance for qcow2 without write-back caching with
> all your improvements?
I haven't done real benchmarks for some time, but my simple test cases
like "run mke2fs on an empty image" have shown great improvement (at
least on IDE, for virtio I haven't understood yet what influences the
size of its requests - you should have received a private mail from Dor
about this). Possibly we could even enable cache=off for qcow2 now.
IIUC, you have a nice setup to measure block performance now. Maybe
you'd like to let it run with qcow2 and cache=wb/none?
Kevin
- [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Kevin Wolf, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Christoph Hellwig, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again,
Kevin Wolf <=
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Avi Kivity, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Kevin Wolf, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Avi Kivity, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Kevin Wolf, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Jamie Lokier, 2009/06/23
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Kevin Wolf, 2009/06/23
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Jamie Lokier, 2009/06/24
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Kevin Wolf, 2009/06/25
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Christoph Hellwig, 2009/06/22
- Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again, Kevin Wolf, 2009/06/22