Messages in this thread Patch in this message | | | From | Michael Zhivich <> | Subject | [PATCH v2] clocksource: tsc: respect tsc bootparam for clocksource_tsc_early | Date | Thu, 24 Oct 2019 13:59:45 -0400 |
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Introduction of clocksource_tsc_early broke functionality of "tsc=reliable" and "tsc=nowatchdog" bootparams, since clocksource_tsc_early is *always* registered with CLOCK_SOURCE_MUST_VERIFY and thus put on the watchdog list.
This frequently causes TSC to be declared unstable during boot:
clocksource: timekeeping watchdog on CPU0: Marking clocksource 'tsc-early' as unstable because the skew is too large: clocksource: 'refined-jiffies' wd_now: fffb7018 wd_last: fffb6e9d mask: ffffffff clocksource: 'tsc-early' cs_now: 68a6a7070f6a0 cs_last: 68a69ab6f74d6 mask: ffffffffffffffff tsc: Marking TSC unstable due to clocksource watchdog
The corresponding elapsed times are cs_nsec=1224152026 and wd_nsec=378942392, so watchdog differs from TSC by 0.84 seconds. Since jiffies is not guaranteed to provide reliable timekeeping due to possibility of missing timer interrupts, this is a false positive.
This issue affects machines running with HPET disabled; otherwise, HPET would be the watchdog for tsc-early clocksource, and this situation would be avoided.
Restore previous behavior by respecting "tsc=reliable" and "tsc=nowatchdog" boot params when registering clocksource_tsc_early.
Fixes: aa83c45762a24 ("x86/tsc: Introduce early tsc clocksource") Signed-off-by: Michael Zhivich <mzhivich@akamai.com> --- arch/x86/kernel/tsc.c | 3 +++ 1 file changed, 3 insertions(+)
Changes from v1: updated commit message, added "Fixes" tag.
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index c59454c382fd..7e322e2daaf5 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1505,6 +1505,9 @@ void __init tsc_init(void) return; } + if (tsc_clocksource_reliable || no_tsc_watchdog) + clocksource_tsc_early.flags &= ~CLOCK_SOURCE_MUST_VERIFY; + clocksource_register_khz(&clocksource_tsc_early, tsc_khz); detect_art(); } -- 2.17.1
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