Messages in this thread | | | Date | Mon, 16 Nov 2009 17:58:04 +0100 | From | Jan Kara <> | Subject | Re: Performance regression in IO scheduler still there |
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On Mon 16-11-09 11:47:44, Jan Kara wrote: > On Thu 12-11-09 15:44:02, Jeff Moyer wrote: > > Jan Kara <jack@suse.cz> writes: > > > > > On Wed 11-11-09 12:43:30, Jeff Moyer wrote: > > >> Jan Kara <jack@suse.cz> writes: > > >> > > >> > Sadly, I don't see the improvement you can see :(. The numbers are the > > >> > same regardless low_latency set to 0: > > >> > 2.6.32-rc5 low_latency = 0: > > >> > 37.39 36.43 36.51 -> 36.776667 0.434920 > > >> > But my testing environment is a plain SATA drive so that probably > > >> > explains the difference... > > >> > > >> I just retested (10 runs for each kernel) on a SATA disk with no NCQ > > >> support and I could not see a difference. I'll try to dig up a disk > > >> that support NCQ. Is that what you're using for testing? > > > I don't think I am. How do I find out? > > > > Good question. ;-) I grep for NCQ in dmesg output and make sure it's > > greater than 0/32. There may be a better way, though. > Message in the logs: > ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300) > ata1.00: ATA-8: Hitachi HTS722016K9SA00, DCDOC54P, max UDMA/133 > ata1.00: 312581808 sectors, multi 16: LBA48 NCQ (depth 0/32) > ata1.00: configured for UDMA/133 > So apparently no NCQ. /sys/block/sda/device/queue_depth shows 1 but I > guess that's just it's way of saying "no NCQ". > > What I thought might make a difference why I'm seeing the drop and you > are not is size of RAM or number of CPUs vs the tiobench file size or > number of threads. I'm running on a machine with 2 GB of RAM, using 4 GB > filesize. The machine has 2 cores and I'm using 16 tiobench threads. I'm > now rerunning tests with various numbers of threads to see how big > difference it makes. OK, here are the numbers (3 runs of each test): 2.6.29: Threads Avg Stddev 1 42.043333 0.860439 2 40.836667 0.322938 4 41.810000 0.114310 8 40.190000 0.419603 16 39.950000 0.403072 32 39.373333 0.766913
2.6.32-rc7: Threads Avg Stddev 1 41.580000 0.403072 2 39.163333 0.374641 4 39.483333 0.400111 8 38.560000 0.106145 16 37.966667 0.098770 32 36.476667 0.032998
So apparently the difference between 2.6.29 and 2.6.32-rc7 increases as the number of threads rises. With how many threads have you been running when using SATA drive and what machine is it? I'm now running a test with larger file size (8GB instead of 4) to see what difference it makes.
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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