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Date: Mon, 23 Apr 2018 14:38:47 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Diego Viola <diego.viola@...il.com>
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 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;
}
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