Kernel Bug Tracker – Bug 13463
Poor SSD performance
Last modified: 2009-06-29 12:01:16 UTC
I have experienced a 3-fold performance cut on read times for my OCZ Vertex 30GB SATAII SSD between kernel versions 2.6.28 and 2.6.29. In 2.6.28, hdparm and other tests showed read speeds of 200-220 MB/s on my Vertex drive. In kernel 2.6.29, I perform the same tests and find read speeds of 70-80 MB/s. I did not benchmark the write speeds.
Kernel architecture is x86_64. Let me know if there's anything else I should check out. I discussed this in the Arch linux forums here: http://bbs.archlinux.org/viewtopic.php?pid=562748#p562748, but we did not make any progress diagnosing the problem.
I marked this as a regression.
Can you please attach boot logs from the two kernels?
Created attachment 21781 [details]
Kernel 2.6.29 log file
Comment on attachment 21781 [details]
Kernel 2.6.29 log file
This file corresponds to booting kernel 2.6.29 when I get slow SSD reads.
Created attachment 21782 [details]
dmesg from booting kernel 2.6.29
I also can submit kernel.log and dmesg from boots of the 184.108.40.206 kernel in which I get full read speeds. I will do this if you think it is necessary.
Yeap, that was what I meant by "the two kernels". Sorry about not being clear.
Also, you attached 25 and 20 byte files which only contain the file names.
Created attachment 21785 [details]
220.127.116.11 kernel boot log.
Created attachment 21786 [details]
18.104.22.168 kernel boot log.
I'm sorry, I should have checked the files before uploading them. The proper files are now uploaded.
Hmm... can't see any ATA related differences. Can you please run the following command as root in 2.6.28 and 29 and report the results?
# dd if=/dev/sda of=/dev/null iflag=direct bs=1M count=1024
In 2.6.28 and 2.6.29 the direct flag gives me 230 MB/s reads.
In the original report, what 'other tests' showed large performance regression other than hdparm? Also, does hdparm give consistent numbers over multiple trials?
dd if=/dev/sda of=/dev/null also gives me read speeds of 70-80 MB/s in 2.6.29, where I get 220 MB/s in 2.6.28.
Hmm... I see. The difference is from far above the block/storage layer. Most likely vm. Andrew, can you please take it? Thanks.
I installed a version of the 2.6.30 kernel and this problem appears to be absent since I got read speeds of 220MB/s. Apparently this problem is isolated to the 2.6.29 kernel.
Heh... so it solved itself. It would be nice to find out which was the culprit. I suppose the right people would already know. Anyways, with 2.6.30 already out of the door, I don't think it's of high priority. Jeff, can you please close this one? Thanks.