On Thu, Apr 08, 2010 at 11:26:15AM -0400, Chris Mason wrote: > With O_DIRECT the writeback rates are very reasonable. I'll work up a > way to pass the barrier down from the guest to btrfs to force logging of > updated metadata when required.
Barriers are implemented in the guest kernel using queue drains and cache flush commands. Qemu maps the cache flush to fdatasync. > > >Once the O_DIRECT read patch is in, you can switch to that, or tell qemu > > >to use a writeback cache instead. > > > > Even with writeback qemu will issue a lot of fsyncs. > > Oh, I didn't see that when I was testing, when does it fsync? When the guest issues a barrier (and it's actually a fdatasync) -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
