On Wed, Nov 28, 2007 at 02:34:02PM +0000, Samuel Thibault wrote: > Daniel P. Berrange, le Wed 28 Nov 2007 14:27:39 +0000, a écrit : > > On Wed, Nov 28, 2007 at 03:02:50PM +0100, Laurent Vivier wrote: > > > These patches allow to open file using O_DIRECT and bypass the host I/O > > > cache. > > > > > > [PATCH 1/2] Add "directio" parameter to "-drive" > > > > > > Using "directio=on" with "-drive" will open the disk image > > > file using "O_DIRECT". > > > > I don't see the point in adding a config param for this. If it provides a > > useful performance improvement (or other benefit) we should enable it by > > default all the time. > > That depends on the mileage of the user. Sometimes it is useful since > it avoids the duplication of page or buffer cache between the guest and > the host, sometimes it is not because the guest is not so i/o friendly > and hence using the host page/buffer cache is useful.
I don't buy that - all OS already do I/O caching because its useful even on baremetal. As an end-user how do you decide whether to turn on the directoio=on/off option or not ? Most people won't notice it & will just run with the default setting - those who do notice are just subjected to trial-and-error to figure out whether the setting is any use. IMHO, QEMU should just pick the best setting. Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|
