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. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- 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
