Messages in this thread | | | Date | Mon, 16 Nov 2009 11:47:44 +0100 | From | Jan Kara <> | Subject | Re: Performance regression in IO scheduler still there |
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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.
Honza
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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