On Sat, Apr 04 2009, Theodore Tso wrote: > On Sat, Apr 04, 2009 at 05:16:50PM +0200, Jens Axboe wrote: > > Big nack on this patch. Ted, this is EXACTLY where I told you we saw big > > write regressions (sqlite performance drops by a factor of 4-5). Do a > > git log on fs/buffer.c and see the original patch (which does what your > > patch does) and the later revert. > > You mean this revert, right? > > commit 78f707bfc723552e8309b7c38a8d0cc51012e813 > Author: Jens Axboe <jens.axboe@xxxxxxxxxx> > Date: Tue Feb 17 13:59:08 2009 +0100 > > block: revert part of 18ce3751ccd488c78d3827e9f6bf54e6322676fb > > The above commit added WRITE_SYNC and switched various places to using > that for committing writes that will be waited upon immediately after > submission. However, this causes a performance regression with AS and CFQ > for ext3 at least, since sync_dirty_buffer() will submit some writes with > WRITE_SYNC while ext3 has sumitted others dependent writes without the sync > flag set. This causes excessive anticipation/idling in the IO scheduler > because sync and async writes get interleaved, causing a big performance > regression for the below test case (which is meant to simulate sqlite > like behaviour).... > > OK, let me test things out first, but note that with the changes that > Linus has already accepted, this may not be an issue --- since we've > now fixed ext3 to submit those dependent writes with the SYNC flag > now. So I'm not sure the performance regression still applies, but > I'll test using the test case supplied in the rest of the commit log > and get back to you. Yep that's the one. I'll throw some testing together here, too. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
