[Bug 190961] New: pvclock_gtod_notify invoked frequently leads to extra cpu load

* [Bug 190961] New: pvclock_gtod_notify invoked frequently leads to extra cpu load
@ 2016-12-23  8:39 bugzilla-daemon
  2016-12-23  8:41 ` [Bug 190961] " bugzilla-daemon
  2016-12-26  4:27 ` bugzilla-daemon
  0 siblings, 2 replies; 3+ messages in thread
From: bugzilla-daemon @ 2016-12-23  8:39 UTC (permalink / raw)
  To: kvm

https://bugzilla.kernel.org/show_bug.cgi?id=190961

            Bug ID: 190961
           Summary: pvclock_gtod_notify invoked frequently leads to extra
                    cpu load
           Product: Virtualization
           Version: unspecified
    Kernel Version: 4.9
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: yu.c.chen@intel.com
        Regression: No

This thread is created for tracking purpose
Currently the notifier of pvclock_gtod_notify() get invoked
frequently due to the periodic update_wall_time(). This might
slow down the system a little bit as there might be redundant
execution code path and unnecessary lock contention
in update_pvclock_gtod(), which was found when I was doing
suspend/resume speed testings. As pvclock_gtod_notify()
should be invoked only when clocksource has changed, according to
Commit 16e8d74d2da9 ("KVM: x86: notifier for clocksource changes")
, either we can add a new notifier for clocksource switch,
or we can simply bypass the following code in pvclock_gtod_notify()
earlier if there is no clocksource switch.

https://patchwork.kernel.org/patch/9487257/

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