arch/x86/kernel/tsc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
TSC could be reset in deep ACPI sleep states, even with invariant TSC.
That's the reason we have sched_clock() save/restore functions, to deal
with this situation. But happens that such functions are guarded with a
check for the stability of sched_clock - if not considered stable, the
save/restore routines aren't executed.
On top of that, we have a clear comment on native_sched_clock() saying
that *even* with TSC unstable, we continue using TSC for sched_clock due
to its speed. In other words, if we have a situation of TSC getting
detected as unstable, it marks the sched_clock as unstable as well,
so subsequent S3 sleep cycles could bring bogus sched_clock values due
to the lack of the save/restore mechanism, causing warnings like this:
[22.954918] ------------[ cut here ]------------
[22.954923] Delta way too big! 18446743750843854390 ts=18446744072977390405 before=322133536015 after=322133536015 write stamp=18446744072977390405
[22.954923] If you just came from a suspend/resume,
[22.954923] please switch to the trace global clock:
[22.954923] echo global > /sys/kernel/tracing/trace_clock
[22.954923] or add trace_clock=global to the kernel command line
[22.954937] WARNING: CPU: 2 PID: 5728 at kernel/trace/ring_buffer.c:2890 rb_add_timestamp+0x193/0x1c0
Notice that the above was reproduced even with "trace_clock=global".
The fix for that is to _always_ save/restore the sched_clock on suspend
cycle _if TSC is used_ as sched_clock - only if we fallback to jiffies
the sched_clock_stable() check becomes relevant to save/restore the
sched_clock.
Cc: stable@vger.kernel.org
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---
arch/x86/kernel/tsc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 34dec0b72ea8..88e5a4ed9db3 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -959,7 +959,7 @@ static unsigned long long cyc2ns_suspend;
void tsc_save_sched_clock_state(void)
{
- if (!sched_clock_stable())
+ if (!static_branch_likely(&__use_tsc) && !sched_clock_stable())
return;
cyc2ns_suspend = sched_clock();
@@ -979,7 +979,7 @@ void tsc_restore_sched_clock_state(void)
unsigned long flags;
int cpu;
- if (!sched_clock_stable())
+ if (!static_branch_likely(&__use_tsc) && !sched_clock_stable())
return;
local_irq_save(flags);
--
2.47.1On 15/02/2025 17:58, Guilherme G. Piccoli wrote: > TSC could be reset in deep ACPI sleep states, even with invariant TSC. > That's the reason we have sched_clock() save/restore functions, to deal > with this situation. But happens that such functions are guarded with a > check for the stability of sched_clock - if not considered stable, the > save/restore routines aren't executed. > > On top of that, we have a clear comment on native_sched_clock() saying > that *even* with TSC unstable, we continue using TSC for sched_clock due > to its speed. In other words, if we have a situation of TSC getting > detected as unstable, it marks the sched_clock as unstable as well, > so subsequent S3 sleep cycles could bring bogus sched_clock values due > to the lack of the save/restore mechanism, causing warnings like this: > > [22.954918] ------------[ cut here ]------------ > [22.954923] Delta way too big! 18446743750843854390 ts=18446744072977390405 before=322133536015 after=322133536015 write stamp=18446744072977390405 > [22.954923] If you just came from a suspend/resume, > [22.954923] please switch to the trace global clock: > [22.954923] echo global > /sys/kernel/tracing/trace_clock > [22.954923] or add trace_clock=global to the kernel command line > [22.954937] WARNING: CPU: 2 PID: 5728 at kernel/trace/ring_buffer.c:2890 rb_add_timestamp+0x193/0x1c0 > > Notice that the above was reproduced even with "trace_clock=global". > > The fix for that is to _always_ save/restore the sched_clock on suspend > cycle _if TSC is used_ as sched_clock - only if we fallback to jiffies > the sched_clock_stable() check becomes relevant to save/restore the > sched_clock. > Hi folks, I would like to ask if possible to add the following tag: Debugged-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com> Cascardo helped me a lot on debugging this issue but I forgot to add it earlier, so nothing more fair than add it now! Thanks, Guilherme > Cc: stable@vger.kernel.org > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> > [...]
The following commit has been merged into the sched/core branch of tip:
Commit-ID: d90c9de9de2f1712df56de6e4f7d6982d358cabe
Gitweb: https://git.kernel.org/tip/d90c9de9de2f1712df56de6e4f7d6982d358cabe
Author: Guilherme G. Piccoli <gpiccoli@igalia.com>
AuthorDate: Sat, 15 Feb 2025 17:58:16 -03:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 21 Feb 2025 15:27:38 +01:00
x86/tsc: Always save/restore TSC sched_clock() on suspend/resume
TSC could be reset in deep ACPI sleep states, even with invariant TSC.
That's the reason we have sched_clock() save/restore functions, to deal
with this situation. But what happens is that such functions are guarded
with a check for the stability of sched_clock - if not considered stable,
the save/restore routines aren't executed.
On top of that, we have a clear comment in native_sched_clock() saying
that *even* with TSC unstable, we continue using TSC for sched_clock due
to its speed.
In other words, if we have a situation of TSC getting detected as unstable,
it marks the sched_clock as unstable as well, so subsequent S3 sleep cycles
could bring bogus sched_clock values due to the lack of the save/restore
mechanism, causing warnings like this:
[22.954918] ------------[ cut here ]------------
[22.954923] Delta way too big! 18446743750843854390 ts=18446744072977390405 before=322133536015 after=322133536015 write stamp=18446744072977390405
[22.954923] If you just came from a suspend/resume,
[22.954923] please switch to the trace global clock:
[22.954923] echo global > /sys/kernel/tracing/trace_clock
[22.954923] or add trace_clock=global to the kernel command line
[22.954937] WARNING: CPU: 2 PID: 5728 at kernel/trace/ring_buffer.c:2890 rb_add_timestamp+0x193/0x1c0
Notice that the above was reproduced even with "trace_clock=global".
The fix for that is to _always_ save/restore the sched_clock on suspend
cycle _if TSC is used_ as sched_clock - only if we fallback to jiffies
the sched_clock_stable() check becomes relevant to save/restore the
sched_clock.
Debugged-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250215210314.351480-1-gpiccoli@igalia.com
---
arch/x86/kernel/tsc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 34dec0b..88e5a4e 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -959,7 +959,7 @@ static unsigned long long cyc2ns_suspend;
void tsc_save_sched_clock_state(void)
{
- if (!sched_clock_stable())
+ if (!static_branch_likely(&__use_tsc) && !sched_clock_stable())
return;
cyc2ns_suspend = sched_clock();
@@ -979,7 +979,7 @@ void tsc_restore_sched_clock_state(void)
unsigned long flags;
int cpu;
- if (!sched_clock_stable())
+ if (!static_branch_likely(&__use_tsc) && !sched_clock_stable())
return;
local_irq_save(flags);On Fri, Feb 21, 2025 at 02:37:42PM -0000, tip-bot2 for Guilherme G. Piccoli wrote: > The following commit has been merged into the sched/core branch of tip: > > Commit-ID: d90c9de9de2f1712df56de6e4f7d6982d358cabe > Gitweb: https://git.kernel.org/tip/d90c9de9de2f1712df56de6e4f7d6982d358cabe > Author: Guilherme G. Piccoli <gpiccoli@igalia.com> > AuthorDate: Sat, 15 Feb 2025 17:58:16 -03:00 > Committer: Ingo Molnar <mingo@kernel.org> > CommitterDate: Fri, 21 Feb 2025 15:27:38 +01:00 > > x86/tsc: Always save/restore TSC sched_clock() on suspend/resume Should this not go into x86/core or somesuch?
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