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Bug 1746282 - qemu-kvm: backport cpuidle-haltpoll support [rhel-7.7.z]
Summary: qemu-kvm: backport cpuidle-haltpoll support [rhel-7.7.z]
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: qemu-kvm-rhev
Version: 7.8
Hardware: Unspecified
OS: Unspecified
high
unspecified
Target Milestone: rc
: ---
Assignee: Marcelo Tosatti
QA Contact: jingzhao
URL:
Whiteboard:
Depends On: 1734502 1759283
Blocks:
TreeView+ depends on / blocked
 
Reported: 2019-08-28 07:26 UTC by RAD team bot copy to z-stream
Modified: 2022-07-09 10:52 UTC (History)
8 users (show)

Fixed In Version: qemu-kvm-rhev-2.12.0-33.el7_7.3
Doc Type: If docs needed, set a value
Doc Text:
Clone Of: 1734502
Environment:
Last Closed: 2019-10-22 15:24:05 UTC
Target Upstream Version:
Embargoed:


Attachments (Terms of Use)
dmesg log of guest (35.53 KB, text/plain)
2019-09-25 06:29 UTC, jingzhao
no flags Details


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2019:3179 0 None None None 2019-10-22 15:24:29 UTC

Description RAD team bot copy to z-stream 2019-08-28 07:26:03 UTC
This bug has been copied from bug #1734502 and has been proposed to be backported to 7.7 z-stream (EUS).

Comment 8 jingzhao 2019-09-25 06:29:18 UTC
Created attachment 1618874 [details]
dmesg log of guest

Comment 16 errata-xmlrpc 2019-10-22 15:24:05 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2019:3179

Comment 17 Marcelo Tosatti 2019-12-11 21:48:00 UTC
Rationale for cpuidle haltpoll driver and usage instructions:

That for baremetal systems, when a CPU waits for a certain event, 
such as a waitqueue notification, the kernel implements this as 
a "mwait" instruction based wait (waiter). This avoids the CPU that wakes
the waiter from sending an IPI (and waiter from processing that IPI).
That can have a significant performance impact (up to 10%) if the 
application is multithreaded, the threads communicate with each
other, and sleep for short intervals of time.

The mwait instruction can't be emulated on KVM easily: so instead
the haltpoll driver busy spins for a specified amount of time 
when a guest vCPU halts.

To enable the driver in a guest, the user has to:

1) Enable the kvm-poll-control CPU flag for the emulated vCPU. For
example, if using qemu directly the relevant command line section 
would be (libvirt configuration should be mentioned):

-cpu SandyBridge,tsc-deadline=on,pmu=off,vmx=off,kvm-poll-control=on

2) Load the cpuidle-haltpoll driver in the guest persistently ("PERSISTENT MODULE LOADING" section of RHEL documentation).

3) Tune the guest_halt_poll_ns module parameter: should be slightly larger
than the average delay the application in question performs. Suggest to benchmark
the app while increasing/decreasing guest_halt_poll_ns.


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