Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: Performance regression in IO scheduler still there | Date | Mon, 16 Nov 2009 12:03:00 -0500 |
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Jan Kara <jack@suse.cz> writes:
> 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.
I've been running with both 8 and 16 threads. The machine has 4 CPUs and 4GB of RAM. I've been testing with an 8GB file size.
Cheers, Jeff
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