sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface

Browse source

Wanpeng Li reported that since the following commit:

  acb04058de ("sched/clock: Fix hotplug crash")

... KVM always runs with unstable sched-clock even though KVM's
kvm_clock _is_ stable.

The problem is that we've tied clear_sched_clock_stable() to the TSC
state, and overlooked that sched_clock() is a paravirt function.

Solve this by doing two things:

 - tie the sched_clock() stable state more clearly to the TSC stable
   state for the normal (!paravirt) case.

 - only call clear_sched_clock_stable() when we mark TSC unstable
   when we use native_sched_clock().

The first means we can actually run with stable sched_clock in more
situations then before, which is good. And since commit:

  12907fbb1a ("sched/clock, clocksource: Add optional cs::mark_unstable() method")

... this should be reliable. Since any detection of TSC fail now results
in marking the TSC unstable.

Reported-by: Wanpeng Li <kernellwp@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: acb04058de ("sched/clock: Fix hotplug crash")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

...

This commit is contained in:

Peter Zijlstra 2017-03-01 15:53:38 +01:00 • committed by Ingo Molnar

parent 0ba87bb27d

commit f94c8d1169

7 changed files with 23 additions and 28 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

4

arch/x86/kernel/cpu/amd.c

View file

2

arch/x86/kernel/cpu/centaur.c

View file

3

arch/x86/kernel/cpu/common.c

View file

1

arch/x86/kernel/cpu/cyrix.c

View file

4

arch/x86/kernel/cpu/intel.c

View file

2

arch/x86/kernel/cpu/transmeta.c

View file

35

arch/x86/kernel/tsc.c

View file