On Fri, 28 Jul 2006 15:54:30 -0400, Rik van Riel wrote: > This is the simple approach to making sure that disk writes actually hit > disk before we tell the guest OS that IO has completed. Thanks to > DMA_MULTI_THREAD the performance still seems to be adequate.
Hi Rik, Right now Fabrice is working on rewriting the block API to be asynchronous. There's been quite a lot of discussion about why using threads isn't a good idea for this (I wish Xen wouldn't use this patch but that's another conversation :-)). The async block API will allow the use of different kinds of async "backends". The default (on Linux) will be posix-aio. I'm currently working on an HTTP backend and will also write a linux-aio (which, of course, will be using O_DIRECT). > A fancier solution would be to make the sync/non-sync behaviour of the > qemu disk backing store tunable from the guest OS, by tuning the IDE disk > write cache on/off with hdparm, and having hw/ide.c call ->fsync functions > in the block backends. With a proper async API, is there any reason why we would want this to be tunable? I don't think there's much of a benefit of prematurely claiming a write is complete especially once the SCSI emulation can support multiple simultaneous requests. I was hoping to just make linux-aio the default if it was available... Regards, Anthony Liguori > I'm willing to code up the fancy solution if people prefer that. _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
