651005 – Excessive fpu swap entering and exiting kvm from host userspace

RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.

Bug 651005 - Excessive fpu swap entering and exiting kvm from host userspace

Summary: Excessive fpu swap entering and exiting kvm from host userspace

Keywords:
Status:	CLOSED ERRATA
Alias:	None
Product:	Red Hat Enterprise Linux 6
Classification:	Red Hat
Component:	kernel
Sub Component:
Version:	6.1
Hardware:	Unspecified
OS:	Unspecified
Priority:	low
Severity:	medium
Target Milestone:	rc
Target Release:	6.1
Assignee:	Karen Noel
QA Contact:	Virtualization Bugs
Docs Contact:
URL:
Whiteboard:
Depends On:
Blocks:	580954
TreeView+	depends on / blocked

Reported:	2010-11-08 16:09 UTC by Avi Kivity
Modified:	2013-01-09 23:18 UTC (History)
CC List:	5 users (show)
Fixed In Version:	kernel-2.6.32-83.el6
Doc Type:	Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed:	2011-05-23 20:28:20 UTC
Target Upstream Version:
Embargoed:

Attachments	(Terms of Use)

Links
System	ID	Private	Priority	Status	Summary	Last Updated
Red Hat Product Errata	RHSA-2011:0542	0	normal	SHIPPED_LIVE	Important: Red Hat Enterprise Linux 6.1 kernel security, bug fix and enhancement update	2011-05-19 11:58:07 UTC

Description Avi Kivity 2010-11-08 16:09:24 UTC

Description of problem:
kvm saves and restores the host fpu, even if the host hasn't been using it.  This is inefficient.

Version-Release number of selected component (if applicable):
2.6.32-80.el6

How reproducible:
Always

Steps to Reproduce:
1. Run a guest
  
Actual results:
Excessive host fpu save/restores

Expected results:
Only swap the host fpu when necessary

Additional info:
Fixed in upstream

Comment 2 RHEL Program Management 2010-11-08 16:59:51 UTC

This request was evaluated by Red Hat Product Management for inclusion
in a Red Hat Enterprise Linux maintenance release. Product Management has 
requested further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed 
products. This request is not yet committed for inclusion in an Update release.

Comment 3 Aristeu Rozanski 2010-11-17 19:47:30 UTC

Patch(es) available on kernel-2.6.32-83.el6

Comment 6 Mike Cao 2011-03-25 08:58:57 UTC

Tried on kernel-2.6.32-122.el6

steps
1.start a RHEL6_64 bit guest with clocksource=acpi_pm
2.run a program that calls gettimeofday() in a loop
# cat test.c
#include <sys/time.h>

void main()
{
  struct timeval tv;
  while(1)
  {
   gettimeofday(&tv,0);
  }
}
3.start system tap to probe save_init_fpu()
eg:
## cat save_init_fpu.stp 
probe begin
{
       printf("start...\n")
}
probe kernel.function("save_init_fpu")
{
       printf("calling..\n")

4.#stap save_init_fpu.stp

Acutal Results
I can NOT get the times save_init_fpu() loaded.


bcao--->avi,

Hi, Could you provide me How to reproduce and verify it ?
thanks,
Mike

Comment 7 Mike Cao 2011-04-15 07:05:04 UTC

Verified this issue by using code review& functional test on 2.6.32-128.el6

steps for code review:
1.download kernel-2.6.32-130.src.rpm
2.compile the src code to see whether patch included

Acutal Results:
check linux-2.6.32-130.el6.x86_64/arch/x86/kvm/x86.c , the patch is included.

steps for functional testing.
1.start linux guest
2.exec a fpu apps more than 12 hours

Actual Results:
Guest works good and no crash occurs.


Based on above ,
This issue has been fixed already.change status to VERIFIED.

Comment 8 errata-xmlrpc 2011-05-23 20:28:20 UTC

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-0542.html

Note You need to log in before you can comment on or make changes to this bug.