On Wed 11-04-12 12:19:43, Mike Christie wrote: > On 04/11/2012 04:40 AM, Michael Tokarev wrote: > > On 10.04.2012 19:13, Jan Kara wrote: > >> > On Tue 10-04-12 10:00:38, Michael Tokarev wrote: > > [] > >>> >> 2.6.38: > >>> >> # dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100 > >>> >> 100+0 records in > >>> >> 100+0 records out > >>> >> 104857600 bytes (105 MB) copied, 1.73126 s, 60.6 MB/s > >>> >> > >>> >> 3.0: > >>> >> # dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100 > >>> >> 100+0 records in > >>> >> 100+0 records out > >>> >> 104857600 bytes (105 MB) copied, 29.4508 s, 3.6 MB/s > >>> >> > >>> >> That's about 20 times difference on direct read from the > >>> >> same - idle - device!! > >> > Huh, that's a huge difference for such a trivial load. So we can rule out > >> > filesystems, writeback, mm. I also wouldn't think it's IO scheduler but > >> > you can always check by comparing dd numbers after > >> > echo none >/sys/block/sdb/queue/scheduler > > Did you try newer 3.X kernels or just 3.0? > > We were hitting a similar problem with iscsi. Same workload and it > started with 2.6.38. I think it turned out to be this issue: > > // thread with issue like what we hit: > http://thread.gmane.org/gmane.linux.kernel/1244680 > > // Patch that I think fixed issue: > commit 3deaa7190a8da38453c4fabd9dec7f66d17fff67 > Author: Shaohua Li <shaohua.li@xxxxxxxxx> > Date: Fri Feb 3 15:37:17 2012 -0800 > > readahead: fix pipeline break caused by block plug I already asked about this but that doesn't seem to be the cause. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
