From f94c8d116997597fc00f0812b0ab9256e7b0c58f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 1 Mar 2017 15:53:38 +0100 Subject: sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface Wanpeng Li reported that since the following commit: acb04058de49 ("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: 12907fbb1a69 ("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 Signed-off-by: Peter Zijlstra (Intel) Cc: Borislav Petkov Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paolo Bonzini Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Fixes: acb04058de49 ("sched/clock: Fix hotplug crash") Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/amd.c | 4 ---- 1 file changed, 4 deletions(-) (limited to 'arch/x86/kernel/cpu/amd.c') diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 4e95b2e0d95f..30d924ae5c34 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -555,10 +555,6 @@ static void early_init_amd(struct cpuinfo_x86 *c) if (c->x86_power & (1 << 8)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); - if (check_tsc_unstable()) - clear_sched_clock_stable(); - } else { - clear_sched_clock_stable(); } /* Bit 12 of 8000_0007 edx is accumulated power mechanism. */ -- cgit v1.2.3