On Mon, Apr 23, 2018 at 08:49:25AM -0300, Diego Viola wrote: > On Mon, Apr 23, 2018 at 8:48 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > On Mon, Apr 23, 2018 at 08:23:24AM -0300, Diego Viola wrote: > >> > That's a Core2 era chip; does it actually have stable TSC ? > >> > >> I'm not sure. > > > > dmesg | grep -i tsc > > > > should be able to tell you. > > [diego@dualcore ~]$ dmesg | grep -i tsc > [ 0.000000] tsc: Fast TSC calibration using PIT > [ 0.016666] tsc: Fast TSC calibration using PIT > [ 0.019999] tsc: Detected 2793.087 MHz processor > [ 0.019999] clocksource: tsc-early: mask: 0xffffffffffffffff > max_cycles: 0x2842be30f1f, max_idle_ns: 440795236296 ns > [ 0.162058] clocksource: Switched to clocksource tsc-early > [ 0.300076] tsc: Marking TSC unstable due to TSC halts in idle > [diego@dualcore ~]$
Much thanks.. I suspect there a bunch of fail when marking unstable before we register clocksource_tsc. The below patch is a bit ugly, but should cure a number of things; it compiles but hasn't otherwise been tested, can you give it a spin? --- - when TSC is unstable and we've already registered tsc-early, don't forget to unregister it; this then leaves us without a tsc clocksource entirely -- which is good. - when we call mark_tsc_unstable() before we've registered clocksource_tsc things go wobbly because it doesn't know about clocksource_tsc_early. Fix that by: - Make clocksource_mark_unstable() work for unregistered clocksources. - which means we have to be able to detect this; use cs.list for this; initialize it empty. - means we also have to place all cs.list manipulation under watchdog_lock -- bit ugly. - Make __clocksource_unstable() de-rate the clocksource. - Call clocksource_mark_unstable() on both tsc and tsc_early. This way we should either end up with a derated tsc clocksource marked UNSTABLE or no tsc clocksource at all, either should result in it not becoming the active clocksource. --- arch/x86/kernel/tsc.c | 22 +++++++++++----------- kernel/time/clocksource.c | 43 +++++++++++++++++++++++++++++++++++-------- 2 files changed, 46 insertions(+), 19 deletions(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 91e6da48cbb6..74392d9d51e0 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1067,6 +1067,7 @@ static struct clocksource clocksource_tsc_early = { .resume = tsc_resume, .mark_unstable = tsc_cs_mark_unstable, .tick_stable = tsc_cs_tick_stable, + .list = LIST_HEAD_INIT(clocksource_tsc_early.list), }; /* @@ -1086,6 +1087,7 @@ static struct clocksource clocksource_tsc = { .resume = tsc_resume, .mark_unstable = tsc_cs_mark_unstable, .tick_stable = tsc_cs_tick_stable, + .list = LIST_HEAD_INIT(clocksource_tsc.list), }; void mark_tsc_unstable(char *reason) @@ -1098,13 +1100,9 @@ void mark_tsc_unstable(char *reason) 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; - } + + clocksource_mark_unstable(&clocksource_tsc_early); + clocksource_mark_unstable(&clocksource_tsc); } EXPORT_SYMBOL_GPL(mark_tsc_unstable); @@ -1244,7 +1242,7 @@ static void tsc_refine_calibration_work(struct work_struct *work) /* Don't bother refining TSC on unstable systems */ if (tsc_unstable) - return; + goto unreg; /* * Since the work is started early in boot, we may be @@ -1297,11 +1295,12 @@ static void tsc_refine_calibration_work(struct work_struct *work) out: if (tsc_unstable) - return; + goto unreg; if (boot_cpu_has(X86_FEATURE_ART)) art_related_clocksource = &clocksource_tsc; clocksource_register_khz(&clocksource_tsc, tsc_khz); +unreg: clocksource_unregister(&clocksource_tsc_early); } @@ -1311,8 +1310,8 @@ static int __init init_tsc_clocksource(void) if (!boot_cpu_has(X86_FEATURE_TSC) || tsc_disabled > 0 || !tsc_khz) return 0; - if (check_tsc_unstable()) - return 0; + if (tsc_unstable) + goto unreg; if (tsc_clocksource_reliable) clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY; @@ -1328,6 +1327,7 @@ static int __init init_tsc_clocksource(void) if (boot_cpu_has(X86_FEATURE_ART)) art_related_clocksource = &clocksource_tsc; clocksource_register_khz(&clocksource_tsc, tsc_khz); +unreg: clocksource_unregister(&clocksource_tsc_early); return 0; } diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 0e974cface0b..f689c9e3ff5e 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -119,6 +119,16 @@ static DEFINE_SPINLOCK(watchdog_lock); static int watchdog_running; static atomic_t watchdog_reset_pending; +static void inline clocksource_watchdog_lock(unsigned long *flags) +{ + spin_lock_irqsave(&watchdog_lock, *flags); +} + +static void inline clocksource_watchdog_unlock(unsigned long *flags) +{ + spin_unlock_irqrestore(&watchdog_lock, *flags); +} + static int clocksource_watchdog_kthread(void *data); static void __clocksource_change_rating(struct clocksource *cs, int rating); @@ -142,6 +152,13 @@ static void __clocksource_unstable(struct clocksource *cs) cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG); cs->flags |= CLOCK_SOURCE_UNSTABLE; + if (list_empty(&cs->list)) { + cs->rating = 0; + return; + } + + __clocksource_change_rating(cs, 0); + if (cs->mark_unstable) cs->mark_unstable(cs); @@ -164,7 +181,7 @@ void clocksource_mark_unstable(struct clocksource *cs) spin_lock_irqsave(&watchdog_lock, flags); if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) { - if (list_empty(&cs->wd_list)) + if (!list_empty(&cs->list) && list_empty(&cs->wd_list)) list_add(&cs->wd_list, &watchdog_list); __clocksource_unstable(cs); } @@ -319,9 +336,8 @@ static void clocksource_resume_watchdog(void) static void clocksource_enqueue_watchdog(struct clocksource *cs) { - unsigned long flags; + INIT_LIST_HEAD(&cs->wd_list); - spin_lock_irqsave(&watchdog_lock, flags); if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { /* cs is a clocksource to be watched. */ list_add(&cs->wd_list, &watchdog_list); @@ -331,7 +347,6 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs) if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; } - spin_unlock_irqrestore(&watchdog_lock, flags); } static void clocksource_select_watchdog(bool fallback) @@ -373,9 +388,6 @@ static void clocksource_select_watchdog(bool fallback) static void clocksource_dequeue_watchdog(struct clocksource *cs) { - unsigned long flags; - - spin_lock_irqsave(&watchdog_lock, flags); if (cs != watchdog) { if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { /* cs is a watched clocksource. */ @@ -384,7 +396,6 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs) clocksource_stop_watchdog(); } } - spin_unlock_irqrestore(&watchdog_lock, flags); } static int __clocksource_watchdog_kthread(void) @@ -779,14 +790,19 @@ EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); */ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) { + unsigned long flags; /* Initialize mult/shift and max_idle_ns */ __clocksource_update_freq_scale(cs, scale, freq); /* Add clocksource to the clocksource list */ mutex_lock(&clocksource_mutex); + + clocksource_watchdog_lock(&flags); clocksource_enqueue(cs); clocksource_enqueue_watchdog(cs); + clocksource_watchdog_unlock(&flags); + clocksource_select(); clocksource_select_watchdog(false); mutex_unlock(&clocksource_mutex); @@ -808,8 +824,13 @@ static void __clocksource_change_rating(struct clocksource *cs, int rating) */ void clocksource_change_rating(struct clocksource *cs, int rating) { + unsigned long flags; + mutex_lock(&clocksource_mutex); + clocksource_watchdog_lock(&flags); __clocksource_change_rating(cs, rating); + clocksource_watchdog_unlock(&flags); + clocksource_select(); clocksource_select_watchdog(false); mutex_unlock(&clocksource_mutex); @@ -821,6 +842,8 @@ EXPORT_SYMBOL(clocksource_change_rating); */ static int clocksource_unbind(struct clocksource *cs) { + unsigned long flags; + if (clocksource_is_watchdog(cs)) { /* Select and try to install a replacement watchdog. */ clocksource_select_watchdog(true); @@ -834,8 +857,12 @@ static int clocksource_unbind(struct clocksource *cs) if (curr_clocksource == cs) return -EBUSY; } + + clocksource_watchdog_lock(&flags); clocksource_dequeue_watchdog(cs); list_del_init(&cs->list); + clocksource_watchdog_lock(&flags); + return 0; }