• Peter Zijlstra's avatar
    sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface · f94c8d11
    Peter Zijlstra authored
    Wanpeng Li reported that since the following commit:
    
      acb04058 ("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:
    
      12907fbb ("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: default avatarWanpeng Li <kernellwp@gmail.com>
    Signed-off-by: default avatarPeter 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: acb04058 ("sched/clock: Fix hotplug crash")
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    f94c8d11
intel.c 24.3 KB