Messages in this thread | | | Date | Thu, 5 Jan 2023 22:56:48 +0800 | From | Feng Tang <> | Subject | Re: [PATCH v5] x86/tsc: Add option to force frequency recalibration with HW timer |
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On Wed, Jan 04, 2023 at 09:46:34AM -0800, Paul E. McKenney wrote: > On Wed, Jan 04, 2023 at 06:32:27AM -0800, Paul E. McKenney wrote: > > On Wed, Jan 04, 2023 at 04:19:38PM +0800, Feng Tang wrote: > > > The kernel assumes that the TSC frequency which is provided by the > > > hardware / firmware via MSRs or CPUID(0x15) is correct after applying > > > a few basic consistency checks. This disables the TSC recalibration > > > against HPET or PM timer. > > > > > > As a result there is no mechanism to validate that frequency in cases > > > where a firmware or hardware defect is suspected. And there was case > > > that some user used atomic clock to measure the TSC frequency and > > > reported an inaccuracy issue, which was later fixed in firmware. > > > > > > Add an option 'recalibrate' for 'tsc' kernel parameter to force the > > > tsc freq recalibration with HPET or PM timer, and warn if the > > > deviation from previous value is more than about 500 PPM, which > > > provides a way to verify the data from hardware / firmware. > > > > > > There is no functional change to existing work flow. > > > > > > Recently there was a real-world case: "The 40ms/s divergence between > > > TSC and HPET was observed on hardware that is quite recent" [1], on > > > that platform the TSC frequence 1896 MHz was got from CPUID(0x15), > > > and the force-reclibration with HPET/PMTIMER both calibrated out > > > value of 1975 MHz, which also matched with check from software > > > 'chronyd', indicating it's a problem of BIOS or firmware. > > > > > > [Thanks tglx for helping improving the commit log] > > > > > > [1]. https://lore.kernel.org/lkml/20221117230910.GI4001@paulmck-ThinkPad-P17-Gen-1/ > > > Signed-off-by: Feng Tang <feng.tang@intel.com> > > > > Nice!!! > > > > Tested-by: Paul E. McKenney <paulmck@kernel.org> > > And I have queued this on -rcu for further review and testing, in > particular, to get it into -next sooner rather than later. Hope that > is OK! > > I was thinking that this recalibrate patch made mine unnecessary: > > b32498162f5c ("clocksource: Verify HPET and PMTMR when TSC unverified") > > But upon further thought, I remembered that what we here at Meta need is > for TSC to remain in use on systems for which it is deemed trustworthy. > The reason is that even a short switch to HPET can terminally annoy some > of our systems. So I must therefore keep b32498162f5c.
Yes, my patch only adds an optional kernel cmdline parameter, and it can't use both HPET and PM_TIMER to do the calibration in one turn. Also, the purpose of the 2 patches are completely different.
Thanks, Feng
> > Thanx, Paul > > > > --- > > > Changelog: > > > > > > since v4: > > > * add the real world case, where the patch helped to root > > > caused a BIOS/FW problem of inaccurate CPUID-0x15 info > > > * rebase against v6.2-rc1 > > > > > > since v3: > > > * add some real world case into commit log > > > * rebase against v6.0-rc1 > > > > > > since v2: > > > * revise the option description in kernel-parameters.txt > > > * rebase against v5.19-rc2 > > > > > > since v1: > > > * refine commit log to state clearly the problem and intention > > > of the patch by copying Thomas' words. > > > > > > .../admin-guide/kernel-parameters.txt | 4 +++ > > > arch/x86/kernel/tsc.c | 34 ++++++++++++++++--- > > > 2 files changed, 34 insertions(+), 4 deletions(-) > > > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > > index 6cfa6e3996cf..d9eb98e748d5 100644 > > > --- a/Documentation/admin-guide/kernel-parameters.txt > > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > > @@ -6369,6 +6369,10 @@ > > > in situations with strict latency requirements (where > > > interruptions from clocksource watchdog are not > > > acceptable). > > > + [x86] recalibrate: force to do frequency recalibration > > > + with a HW timer (HPET or PM timer) for systems whose > > > + TSC frequency comes from HW or FW through MSR or CPUID(0x15), > > > + and warn if the difference is more than 500 ppm. > > > > > > tsc_early_khz= [X86] Skip early TSC calibration and use the given > > > value instead. Useful when the early TSC frequency discovery > > > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c > > > index a78e73da4a74..92bbc4a6b3fc 100644 > > > --- a/arch/x86/kernel/tsc.c > > > +++ b/arch/x86/kernel/tsc.c > > > @@ -48,6 +48,8 @@ static DEFINE_STATIC_KEY_FALSE(__use_tsc); > > > > > > int tsc_clocksource_reliable; > > > > > > +static int __read_mostly tsc_force_recalibrate; > > > + > > > static u32 art_to_tsc_numerator; > > > static u32 art_to_tsc_denominator; > > > static u64 art_to_tsc_offset; > > > @@ -303,6 +305,8 @@ static int __init tsc_setup(char *str) > > > mark_tsc_unstable("boot parameter"); > > > if (!strcmp(str, "nowatchdog")) > > > no_tsc_watchdog = 1; > > > + if (!strcmp(str, "recalibrate")) > > > + tsc_force_recalibrate = 1; > > > return 1; > > > } > > > > > > @@ -1374,6 +1378,25 @@ static void tsc_refine_calibration_work(struct work_struct *work) > > > else > > > freq = calc_pmtimer_ref(delta, ref_start, ref_stop); > > > > > > + /* Will hit this only if tsc_force_recalibrate has been set */ > > > + if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) { > > > + > > > + /* Warn if the deviation exceeds 500 ppm */ > > > + if (abs(tsc_khz - freq) > (tsc_khz >> 11)) { > > > + pr_warn("Warning: TSC freq calibrated by CPUID/MSR differs from what is calibrated by HW timer, please check with vendor!!\n"); > > > + pr_info("Previous calibrated TSC freq:\t %lu.%03lu MHz\n", > > > + (unsigned long)tsc_khz / 1000, > > > + (unsigned long)tsc_khz % 1000); > > > + } > > > + > > > + pr_info("TSC freq recalibrated by [%s]:\t %lu.%03lu MHz\n", > > > + hpet ? "HPET" : "PM_TIMER", > > > + (unsigned long)freq / 1000, > > > + (unsigned long)freq % 1000); > > > + > > > + return; > > > + } > > > + > > > /* Make sure we're within 1% */ > > > if (abs(tsc_khz - freq) > tsc_khz/100) > > > goto out; > > > @@ -1407,8 +1430,10 @@ static int __init init_tsc_clocksource(void) > > > if (!boot_cpu_has(X86_FEATURE_TSC) || !tsc_khz) > > > return 0; > > > > > > - if (tsc_unstable) > > > - goto unreg; > > > + if (tsc_unstable) { > > > + clocksource_unregister(&clocksource_tsc_early); > > > + return 0; > > > + } > > > > > > if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3)) > > > clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP; > > > @@ -1421,9 +1446,10 @@ 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; > > > + > > > + if (!tsc_force_recalibrate) > > > + return 0; > > > } > > > > > > schedule_delayed_work(&tsc_irqwork, 0); > > > -- > > > 2.34.1 > > >
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