From a786ef152cdcfebc923a67f63c7815806eefcf81 Mon Sep 17 00:00:00 2001 From: Daniel Vacek Date: Mon, 5 Nov 2018 18:10:40 +0100 Subject: [PATCH 1/2] x86/tsc: Make calibration refinement more robust The threshold in tsc_read_refs() is constant which may favor slower CPUs but may not be optimal for simple reading of reference on faster ones. Hence make it proportional to tsc_khz when available to compensate for this. The threshold guards against any disturbance like IRQs, NMIs, SMIs or CPU stealing by host on guest systems so rename it accordingly and fix comments as well. Also on some systems there is noticeable DMI bus contention at some point during boot keeping the readout failing (observed with about one in ~300 boots when testing). In that case retry also the second readout instead of simply bailing out unrefined. Usually the next second the readout returns fast just fine without any issues. Signed-off-by: Daniel Vacek Signed-off-by: Thomas Gleixner Cc: Borislav Petkov Cc: "H. Peter Anvin" Link: https://lkml.kernel.org/r/1541437840-29293-1-git-send-email-neelx@redhat.com --- arch/x86/kernel/tsc.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index e9f777bfed40..3fae23834069 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -297,15 +297,16 @@ static int __init tsc_setup(char *str) __setup("tsc=", tsc_setup); -#define MAX_RETRIES 5 -#define SMI_TRESHOLD 50000 +#define MAX_RETRIES 5 +#define TSC_DEFAULT_THRESHOLD 0x20000 /* - * Read TSC and the reference counters. Take care of SMI disturbance + * Read TSC and the reference counters. Take care of any disturbances */ static u64 tsc_read_refs(u64 *p, int hpet) { u64 t1, t2; + u64 thresh = tsc_khz ? tsc_khz >> 5 : TSC_DEFAULT_THRESHOLD; int i; for (i = 0; i < MAX_RETRIES; i++) { @@ -315,7 +316,7 @@ static u64 tsc_read_refs(u64 *p, int hpet) else *p = acpi_pm_read_early(); t2 = get_cycles(); - if ((t2 - t1) < SMI_TRESHOLD) + if ((t2 - t1) < thresh) return t2; } return ULLONG_MAX; @@ -703,15 +704,15 @@ static unsigned long pit_hpet_ptimer_calibrate_cpu(void) * zero. In each wait loop iteration we read the TSC and check * the delta to the previous read. We keep track of the min * and max values of that delta. The delta is mostly defined - * by the IO time of the PIT access, so we can detect when a - * SMI/SMM disturbance happened between the two reads. If the + * by the IO time of the PIT access, so we can detect when + * any disturbance happened between the two reads. If the * maximum time is significantly larger than the minimum time, * then we discard the result and have another try. * * 2) Reference counter. If available we use the HPET or the * PMTIMER as a reference to check the sanity of that value. * We use separate TSC readouts and check inside of the - * reference read for a SMI/SMM disturbance. We dicard + * reference read for any possible disturbance. We dicard * disturbed values here as well. We do that around the PIT * calibration delay loop as we have to wait for a certain * amount of time anyway. @@ -744,7 +745,7 @@ static unsigned long pit_hpet_ptimer_calibrate_cpu(void) if (ref1 == ref2) continue; - /* Check, whether the sampling was disturbed by an SMI */ + /* Check, whether the sampling was disturbed */ if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX) continue; @@ -1268,7 +1269,7 @@ static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work); */ static void tsc_refine_calibration_work(struct work_struct *work) { - static u64 tsc_start = -1, ref_start; + static u64 tsc_start = ULLONG_MAX, ref_start; static int hpet; u64 tsc_stop, ref_stop, delta; unsigned long freq; @@ -1283,14 +1284,15 @@ static void tsc_refine_calibration_work(struct work_struct *work) * delayed the first time we expire. So set the workqueue * again once we know timers are working. */ - if (tsc_start == -1) { + if (tsc_start == ULLONG_MAX) { +restart: /* * Only set hpet once, to avoid mixing hardware * if the hpet becomes enabled later. */ hpet = is_hpet_enabled(); - schedule_delayed_work(&tsc_irqwork, HZ); tsc_start = tsc_read_refs(&ref_start, hpet); + schedule_delayed_work(&tsc_irqwork, HZ); return; } @@ -1300,9 +1302,9 @@ static void tsc_refine_calibration_work(struct work_struct *work) if (ref_start == ref_stop) goto out; - /* Check, whether the sampling was disturbed by an SMI */ - if (tsc_start == ULLONG_MAX || tsc_stop == ULLONG_MAX) - goto out; + /* Check, whether the sampling was disturbed */ + if (tsc_stop == ULLONG_MAX) + goto restart; delta = tsc_stop - tsc_start; delta *= 1000000LL; From d999c0ec2498e54b9328db6b2c1037710025add1 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Fri, 30 Nov 2018 13:14:50 -0800 Subject: [PATCH 2/2] x86/hpet: Remove unused FSEC_PER_NSEC define The FSEC_PER_NSEC macro has had zero users since commit ab0e08f15d23 ("x86: hpet: Cleanup the clockevents init and register code"). Remove it. Signed-off-by: Roland Dreier Signed-off-by: Borislav Petkov Acked-by: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: x86-ml Link: https://lkml.kernel.org/r/20181130211450.5200-1-roland@purestorage.com --- arch/x86/kernel/hpet.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index b0acb22e5a46..dfd3aca82c61 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -21,10 +21,6 @@ #define HPET_MASK CLOCKSOURCE_MASK(32) -/* FSEC = 10^-15 - NSEC = 10^-9 */ -#define FSEC_PER_NSEC 1000000L - #define HPET_DEV_USED_BIT 2 #define HPET_DEV_USED (1 << HPET_DEV_USED_BIT) #define HPET_DEV_VALID 0x8