69 lines
2.8 KiB
Diff
69 lines
2.8 KiB
Diff
From 7a0abf17cceb511425b7af34291243b4a270e770 Mon Sep 17 00:00:00 2001
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From: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
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Date: Sat, 15 Feb 2025 17:58:16 -0300
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Subject: x86/tsc: Always save/restore TSC sched_clock() on suspend/resume
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TSC could be reset in deep ACPI sleep states, even with invariant TSC.
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That's the reason we have sched_clock() save/restore functions, to deal
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with this situation. But what happens is that such functions are guarded
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with a check for the stability of sched_clock - if not considered stable,
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the save/restore routines aren't executed.
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On top of that, we have a clear comment in native_sched_clock() saying
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that *even* with TSC unstable, we continue using TSC for sched_clock due
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to its speed.
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In other words, if we have a situation of TSC getting detected as unstable,
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it marks the sched_clock as unstable as well, so subsequent S3 sleep cycles
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could bring bogus sched_clock values due to the lack of the save/restore
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mechanism, causing warnings like this:
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[22.954918] ------------[ cut here ]------------
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[22.954923] Delta way too big! 18446743750843854390 ts=18446744072977390405 before=322133536015 after=322133536015 write stamp=18446744072977390405
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[22.954923] If you just came from a suspend/resume,
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[22.954923] please switch to the trace global clock:
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[22.954923] echo global > /sys/kernel/tracing/trace_clock
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[22.954923] or add trace_clock=global to the kernel command line
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[22.954937] WARNING: CPU: 2 PID: 5728 at kernel/trace/ring_buffer.c:2890 rb_add_timestamp+0x193/0x1c0
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Notice that the above was reproduced even with "trace_clock=global".
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The fix for that is to _always_ save/restore the sched_clock on suspend
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cycle _if TSC is used_ as sched_clock - only if we fallback to jiffies
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the sched_clock_stable() check becomes relevant to save/restore the
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sched_clock.
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Debugged-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
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Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Cc: stable@vger.kernel.org
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Link: https://lore.kernel.org/r/20250215210314.351480-1-gpiccoli@igalia.com
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---
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arch/x86/kernel/tsc.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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--- a/arch/x86/kernel/tsc.c
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+++ b/arch/x86/kernel/tsc.c
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@@ -959,7 +959,7 @@ static unsigned long long cyc2ns_suspend
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void tsc_save_sched_clock_state(void)
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{
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- if (!sched_clock_stable())
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+ if (!static_branch_likely(&__use_tsc) && !sched_clock_stable())
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return;
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cyc2ns_suspend = sched_clock();
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@@ -979,7 +979,7 @@ void tsc_restore_sched_clock_state(void)
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unsigned long flags;
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int cpu;
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- if (!sched_clock_stable())
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+ if (!static_branch_likely(&__use_tsc) && !sched_clock_stable())
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return;
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local_irq_save(flags);
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