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Date: Mon, 23 Apr 2018 10:24:33 -0300
From: Diego Viola <diego.viola@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de,
len.brown@...el.com, rui.zhang@...el.com,
"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: Experiencing freezes with kernel 4.16.3 on a desktop with E5500
CPU (bisect included)
On Mon, Apr 23, 2018 at 9:49 AM, Diego Viola <diego.viola@...il.com> wrote:
> On Mon, Apr 23, 2018 at 9:38 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>> On Mon, Apr 23, 2018 at 08:49:25AM -0300, Diego Viola wrote:
>>> On Mon, Apr 23, 2018 at 8:48 AM, Peter Zijlstra <peterz@...radead.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@...lcore ~]$ 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@...lcore ~]$
>>
>> 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;
>> }
>>
>
> Yes, compiling the kernel (torvalds/linux.git HEAD) with your patch right now.
>
> Thanks,
> Diego
I tried your patch with 4.17-rc2 but now my system won't boot, I
believe it fails at early booting.
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