Bug 13463

Summary:	Poor SSD performance
Product:	IO/Storage	Reporter:	Jake (ellowitz)
Component:	Serial ATA	Assignee:	Jeff Garzik (jgarzik)
Status:	CLOSED PATCH_ALREADY_AVAILABLE
Severity:	normal	CC:	akpm, alan, rjw, tj
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	2.6.29.4	Subsystem:
Regression:	Yes	Bisected commit-id:
Bug Depends on:
Bug Blocks:	12398
Attachments:	Kernel 2.6.29 log file dmesg from booting kernel 2.6.29 2.6.29.4 kernel boot log. 2.6.28.10 kernel boot log.

Description Jake 2009-06-05 17:37:07 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.

Comment 1 Andrew Morton 2009-06-05 17:48:17 UTC

I marked this as a regression.

Comment 2 Tejun Heo 2009-06-07 03:12:26 UTC

Can you please attach boot logs from the two kernels?

Comment 3 Jake 2009-06-07 04:36:12 UTC

Created attachment 21781 [details]
Kernel 2.6.29 log file

Comment 4 Jake 2009-06-07 04:37:13 UTC

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.

Comment 5 Jake 2009-06-07 04:37:52 UTC

Created attachment 21782 [details]
dmesg from booting kernel 2.6.29

Comment 6 Jake 2009-06-07 04:39:08 UTC

I also can submit kernel.log and dmesg from boots of the 2.6.28.10 kernel in which I get full read speeds. I will do this if you think it is necessary.

Comment 7 Tejun Heo 2009-06-07 04:41:29 UTC

Yeap, that was what I meant by "the two kernels".  Sorry about not being clear.

Comment 8 Tejun Heo 2009-06-07 04:42:32 UTC

Also, you attached 25 and 20 byte files which only contain the file names.

Comment 9 Jake 2009-06-07 12:20:44 UTC

Created attachment 21785 [details]
2.6.29.4 kernel boot log.

Comment 10 Jake 2009-06-07 12:22:57 UTC

Created attachment 21786 [details]
2.6.28.10 kernel boot log.

Comment 11 Jake 2009-06-07 12:23:36 UTC

I'm sorry, I should have checked the files before uploading them. The proper files are now uploaded.

Comment 12 Tejun Heo 2009-06-08 02:45:02 UTC

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

Thanks.

Comment 13 Jake 2009-06-08 02:49:32 UTC

In 2.6.28 and 2.6.29 the direct flag gives me 230 MB/s reads.

Comment 14 Tejun Heo 2009-06-08 04:02:41 UTC

In the original report, what 'other tests' showed large performance regression other than hdparm?  Also, does hdparm give consistent numbers over multiple trials?

Comment 15 Jake 2009-06-08 04:04:49 UTC

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.

Comment 16 Tejun Heo 2009-06-08 04:09:09 UTC

Hmm... I see.  The difference is from far above the block/storage layer.  Most likely vm.  Andrew, can you please take it?  Thanks.

Comment 17 Jake 2009-06-16 04:01:25 UTC

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.

Comment 18 Tejun Heo 2009-06-17 06:24:25 UTC

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.