Bug 677005

Summary:	CFQ IO SCHED bad performance
Product:	Red Hat Enterprise Linux 5	Reporter:	Yuri Arabadji <yuri>
Component:	kernel	Assignee:	Red Hat Kernel Manager <kernel-mgr>
Status:	CLOSED WONTFIX	QA Contact:	Red Hat Kernel QE team <kernel-qe>
Severity:	high	Docs Contact:
Priority:	unspecified
Version:	5.5	CC:	rwheeler, yuri
Target Milestone:	rc
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2014-06-02 13:09:27 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:

Description Yuri Arabadji 2011-02-12 14:12:47 UTC

I've got a server with 3ware RAID card and a recent RHEL kernel on it. I've tried to update RAID firmware, but getting same slowness.  

Here's how you reproduce it:
1. open 2 shells
2.  dd reading from device in first shell
3.  do some I/O in second shell.
4. change scheduler to "deadline". Repeat 1-3, notice the huge difference.

The kernel version is: 2.6.18-238.1.1.el5

Here are the results of tests:

=========================================================
freshly booted machine

<<launch dd in 1st shell>>
[root@r1d1-28 ~]# cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]
[root@r1d1-28 ~]# time yum search sadfaserZ >/dev/null
Warning: No matches found for: sadfaserZ

real    0m24.948s
user    0m0.344s
sys     0m0.121s
<<stop dd in 1st shell>>
[root@r1d1-28 ~]# echo 0 > /sys/block/sda/queue/iosched/slice_idle
[root@r1d1-28 ~]# echo 1 | tee /proc/sys/vm/drop_caches
1
<<launch dd in 1st shell>>
[root@r1d1-28 ~]# time yum search sadfaserZ >/dev/null
Warning: No matches found for: sadfaserZ

real    0m3.178s
user    0m0.368s
sys     0m0.136s
<<stop dd in 1st shell>>
[root@r1d1-28 ~]# echo deadline  >  /sys/block/sda/queue/scheduler 
[root@r1d1-28 ~]# echo 1 | tee /proc/sys/vm/drop_caches
1
<<launch dd in 1st shell>>
[root@r1d1-28 ~]# time yum search sadfaserZ >/dev/null
Warning: No matches found for: sadfaserZ

real    0m2.936s
user    0m0.348s
sys     0m0.131s
=========================================================

I used "yum" because it does db-like i/o, but it doesn't matter - it could be anything requesting disk access. What would you recommend in this situation? I thought CFQ was fixed previous year in -192.

Thanks!

Comment 1 Ric Wheeler 2011-02-12 16:16:31 UTC

Hi Yuri,

Can you please open a ticket through Red Hat support if you have a subscription?

Red Hat bugzilla is not meant as the first line of customer support, thanks!

Comment 2 Yuri Arabadji 2011-02-12 17:09:20 UTC

I can't. I don't have a subscription. The same is observed with latest centos 5.5 kernel. The problem seems to be limited to this particular server, although I've tested only other two. Will get back once I have more info. But again, it happens only with CFQ, see my "test output".

Comment 3 Ric Wheeler 2011-02-12 17:59:09 UTC

Hi Yuri,

If you don't have a subscription, the best way to get help is to post things to the upstream mailing list (for CFQ issues, Jens Axboe is the upstream lead and the right list is probably linux-kernel.org).

Thanks!

Comment 4 RHEL Program Management 2014-03-07 12:45:58 UTC

This bug/component is not included in scope for RHEL-5.11.0 which is the last RHEL5 minor release. This Bugzilla will soon be CLOSED as WONTFIX (at the end of RHEL5.11 development phase (Apr 22, 2014)). Please contact your account manager or support representative in case you need to escalate this bug.

Comment 5 RHEL Program Management 2014-06-02 13:09:27 UTC

Thank you for submitting this request for inclusion in Red Hat Enterprise Linux 5. We've carefully evaluated the request, but are unable to include it in RHEL5 stream. If the issue is critical for your business, please provide additional business justification through the appropriate support channels (https://access.redhat.com/site/support).