Kernel Bug Tracker – Bug 13726
fio sync read 4k block size 35% regression
Last modified: 2009-08-03 20:57:01 UTC
Subject : fio sync read 4k block size 35% regression
Submitter : "Zhang, Yanmin" <firstname.lastname@example.org>
Date : 2009-07-01 11:25
References : http://lkml.org/lkml/2009/6/30/679
Handled-By : Wu Fengguang <email@example.com>
This entry is being used for tracking a regression from 2.6.30. Please don't
close it until the problem is fixed in the mainline.
Author: Wu Fengguang <firstname.lastname@example.org>
Date: Tue Jun 16 15:31:24 2009 -0700
readahead: remove sync/async readahead call dependency
First-Bad-Commit : 51daa88ebd8e0d437289f589af29d4b39379ea76
On Tuesday 07 July 2009, Zhang, Yanmin wrote:
> On Tue, 2009-07-07 at 02:01 +0200, Rafael J. Wysocki wrote:
> > This message has been generated automatically as a part of a report
> > of recent regressions.
> > The following bug entry is on the current list of known regressions
> > from 2.6.30. Please verify if it still should be listed and let me know
> > (either way).
> > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13726
> > Subject : fio sync read 4k block size 35% regression
> > Submitter : Zhang, Yanmin <email@example.com>
> > Date : 2009-07-01 11:25 (6 days old)
> I'm still working on it now. The new testing against 2.6.31-rc2 is ongoing.
> fio sync/mmap read has new behavior. I did collect some data. But suddenly
> with new created data, the fio_sync_read_4k regression disappeared, while
> fio_mmap_read is still there. Originally, the testing and bisect were stable.
> Let me check what happens firstly.
I found something new with the workload.
1) The parameters of FIO I used cause fio to read files round-robin and every I/O only consists of a block; original, I imagine it read a complete file, then switch to another file;
2) fio is a typical disk I/O testing benchmark, so cpu utilization is very little. I found such cpu C states have big impact on such workload results, especially on Nehalem machines. On my Nehalem machine, cpu enters C2/C3 frequently which causes a long latency to restore to C0 state. It hurts fio result on Nehalem machine. I add idle=poll to kernel boot command line now.
3) FengGuang thinks round-robin is a good test scenario, so I add new sub-cases, including read sequential and read round-robin.
I would like to close the report now. If finding new issues with new revised test cases, I will open new reports.