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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] Default cache mode |
Date: | Wed, 29 Jun 2011 10:26:52 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10 |
On 06/29/2011 09:52 AM, Christoph Hellwig wrote:
On Wed, Jun 29, 2011 at 09:20:03AM -0500, Anthony Liguori wrote:Sorry, I meant having a new cache option (maybe diskcache). Semantics would be: diskcache=on,wce=on 0 diskcache=on,wce=off O_SYNC diskcache=off,wce=on O_DIRECT diskcache=off,wce=off O_DIRECT | O_SYNC ignore_flush could be another option too.Please make it two options instead of a two-dimensional one.
Yeah, that was just for the table. diskcache/hostcache belongs in -drive, wce belongs in -device.
E.g. e hostcache=[on,off] option for the drive command line, where fake is the equivalent of the current code together withI think developers usually want diskcache=on but I also agree that usually in production, you want diskcache=off.Why would you want to not use O_DIRECT as a developer?
Relaunching the same guest: cache=writethrough: real 0m9.500s user 0m4.720s sys 0m3.780s cache=none: real 0m15.263s user 0m4.870s sys 0m6.390sIf you're doing kernel development where you're frequently launching the same guest with a different kernel, it using the page cache makes a big difference in guest boot time.
Regards, Anthony Liguori
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