On Tue, Mar 12, 2013 at 09:21:51AM +0100, Paolo Bonzini wrote: > Il 12/03/2013 02:31, Asias He ha scritto: > > On Mon, Mar 11, 2013 at 12:36:37PM +0100, Paolo Bonzini wrote: > >> Il 11/03/2013 06:09, Asias He ha scritto: > >>> This patch makes vhost_scsi_flush() wait for all the pending requests > >>> issued before the flush operation to be finished. > >> > >> There is no protection against issuing concurrent flush operations. If > >> we later would like to make the flush a ioctl (for example for migration > >> purposes), it would be confusing, and I'm not sure how you could extend > >> the during_flush machinery. > > > > vhost_scsi_flush() is called under the vs->dev.mutex lock. > > Ah, ok. > > >> What about making vhost_scsi_flush() wait for all pending requests, > >> including those issues during the flush operation? > > > > This will take unbonded time if guest keep sending requests. > > Yes, that's correct, but flush doesn't really mean much if new requests > can come in (unlike _cache_ flushes like SYNCHRONIZE CACHE). In the end > you'll have to stop the VM first and then issue the flush. At this > point, it does not change much if you wait for previous requests or all > requests, and I suspect that waiting for all requests simplifies the > code noticeably. Michael, any comments? You suggested flushing of previous requests other than all the requests when I was doing vhost-blk. > >> Then you can easily > >> support concurrent flushes; just add a waitqueue and wake_up_all at the > >> end of the flush operation. > > > > I am not sure why we want concurrent flushes. The flush thing is > > already getting complex. > > Yeah, it is too complex... > > Paolo > > >> BTW, adding such a ioctl as part of this patch would probably be a good > >> thing to do anyway. > >> > >> Paolo > > > -- Asias -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
