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/tsc.c | 35 +++++++++++++++++++++++------------ 1 file changed, 23 insertions(+), 12 deletions(-) (limited to 'arch/x86/kernel/tsc.c') diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 2724dc82f992..911129fda2f9 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -326,9 +326,16 @@ unsigned long long sched_clock(void) { return paravirt_sched_clock(); } + +static inline bool using_native_sched_clock(void) +{ + return pv_time_ops.sched_clock == native_sched_clock; +} #else unsigned long long sched_clock(void) __attribute__((alias("native_sched_clock"))); + +static inline bool using_native_sched_clock(void) { return true; } #endif int check_tsc_unstable(void) @@ -1111,8 +1118,10 @@ static void tsc_cs_mark_unstable(struct clocksource *cs) { if (tsc_unstable) return; + tsc_unstable = 1; - clear_sched_clock_stable(); + if (using_native_sched_clock()) + clear_sched_clock_stable(); disable_sched_clock_irqtime(); pr_info("Marking TSC unstable due to clocksource watchdog\n"); } @@ -1134,18 +1143,20 @@ static struct clocksource clocksource_tsc = { void mark_tsc_unstable(char *reason) { - if (!tsc_unstable) { - tsc_unstable = 1; + if (tsc_unstable) + return; + + tsc_unstable = 1; + if (using_native_sched_clock()) clear_sched_clock_stable(); - disable_sched_clock_irqtime(); - pr_info("Marking TSC unstable due to %s\n", reason); - /* Change only the rating, when not registered */ - if (clocksource_tsc.mult) - clocksource_mark_unstable(&clocksource_tsc); - else { - clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE; - clocksource_tsc.rating = 0; - } + disable_sched_clock_irqtime(); + pr_info("Marking TSC unstable due to %s\n", reason); + /* Change only the rating, when not registered */ + if (clocksource_tsc.mult) { + clocksource_mark_unstable(&clocksource_tsc); + } else { + clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE; + clocksource_tsc.rating = 0; } } -- cgit v1.2.3