On 2010-06-17 13:49, Matthew Wilcox wrote: > On Thu, Jun 17, 2010 at 10:10:18AM +0200, Jens Axboe wrote: >> On 2010-06-17 09:54, Christoph Hellwig wrote: >>> Filesystems assume that DISCARD_BARRIER are full barriers, so that they >>> don't have to track in-progress discard operation when submitting new I/O. >>> But currently we only treat them as elevator barriers, which don't >>> actually do the nessecary queue drains. >>> >>> Also remove the unlikely around both the DISCARD and BARRIER requests - >>> the happen far too often for a static mispredict. >> >> Thanks, applied. There was a recent problem report on btrfs using >> discard, could possibly explain it if Chris assumed it was a full >> barrier. > > If it was on real hardware (ie a SATA disc), it can't be this problem, > since TRIM isn't NCQ so there was already an implicit queue drain ahead > and behind the TRIM. I hear rumours of an NCQ TRIM coming 'RSN', but > haven't seen any details on it yet. Good point, it will drain the queue on SATA of course. The problem was reported on MMC, I doubt the do queuing at all (though I have not checked). -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
