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 with

I 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     0m6.390s

If 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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