Bug 585247

Summary:	CFQ regression in 5.5 with sequential workloads
Product:	Red Hat Enterprise Linux 5	Reporter:	Vivek Goyal <vgoyal>
Component:	kernel	Assignee:	Jeff Moyer <jmoyer>
Status:	CLOSED INSUFFICIENT_DATA	QA Contact:	Red Hat Kernel QE team <kernel-qe>
Severity:	medium	Docs Contact:
Priority:	low
Version:	5.5	CC:	jmoyer
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:	2011-02-07 16:38:39 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Vivek Goyal 2010-04-23 14:24:11 UTC

Description of problem:

I was running some sequential workloads with CFQ, and I see a regression in 5.5
as compared to 5.4

I ran iostest with 5.4 and 5.5 kernels on machine storageqe02.rhts.eng.bos.redhat.com.

Host=storageqe-02.rhts.eng.bos.redhat.com Kernel=2.6.18-164.el5         
DIR=/mnt/iostestmnt/fio        DEV=/dev/cciss/c1d0p1         
Workload=bsr      iosched=cfq     Filesz=1G   bs=8K   
=========================================================================
job       Set NR  ReadBW(KB/s)   MaxClat(us)    WriteBW(KB/s)  MaxClat(us)    
---       --- --  ------------   -----------    -------------  -----------    
bsr       1   1   230014         52873          0              0              
bsr       1   2   173762         115622         0              0              
bsr       1   4   175933         323484         0              0              
bsr       1   8   171647         1215375        0              0              
bsr       1   16  168934         2859577        0              0              

Host=storageqe-02.rhts.eng.bos.redhat.com Kernel=2.6.18-191.el5         
DIR=/mnt/iostestmnt/fio        DEV=/dev/cciss/c1d0p1         
Workload=bsr      iosched=cfq     Filesz=1G   bs=8K   
=========================================================================
job       Set NR  ReadBW(KB/s)   MaxClat(us)    WriteBW(KB/s)  MaxClat(us)    
---       --- --  ------------   -----------    -------------  -----------    
bsr       1   1   174919         25672          0              0              
bsr       1   2   45996          126272         0              0              
bsr       1   4   46002          621047         0              0              
bsr       1   8   48712          823121         0              0              
bsr       1   16  46985          2082693        0              0              


Version-Release number of selected component (if applicable):

2.6.18-191.el5

How reproducible:

Always

Steps to Reproduce:
1. Run iostest
2.
3.
  
Actual results:


Expected results:


Additional info:

Comment 1 Jeff Moyer 2010-07-22 21:03:57 UTC

iostest seems to rely on bashisms that don't exist in my RHEL 5 version of bash.  So, I just ran a fio job file for 1 2 4 and 8 sequential readers.  I don't see this performance issue on my storage, an IBM 2810XIV.  Maybe I got the fio job file syntax wrong:

[global]
size=4096m
directory=/mnt/test/
ioscheduler=deadline   # changed this between runs
invalidate=1
runtime=30
time_based
rw=read

[bsr1]
nrfiles=1

[bsr2]
stonewall
nrfiles=2

[bsr4]
stonewall
nrfiles=4

[bsr8]
stonewall
nrfiles=8

I tested with kernel 2.6.18-194.el5.

Comment 2 Jeff Moyer 2010-08-26 19:20:38 UTC

I've tried to reproduce this on my HP EVA, and I am unable to.  In fact, the 5.5 kernel seems to perform better than the 5.4 kernel.  I'm not sure what to do with this bug at this point.

Comment 3 Jeff Moyer 2011-02-07 16:38:39 UTC

Vivek, I'm closing this bug.  If you can reproduce it, feel free to re-open it.

Thanks!