From 4774d06097e524913fbd4ffcea3307275c5215d1 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 25 Jan 2022 13:37:45 +0100 Subject: [PATCH] x86/time: use relative counts in calibration loops MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Looping until reaching/exceeding a certain value is error prone: If the target value is close enough to the wrapping point, the loop may not terminate at all. Switch to using delta values, which then allows to fold the two loops each into just one. Fixes: 93340297802b ("x86/time: calibrate TSC against platform timer") Reported-by: Roger Pau Monné Signed-off-by: Jan Beulich Reviewed-by: Roger Pau Monné master commit: 467191641d2a2fd2e43b3ae7b80399f89d339980 master date: 2022-01-13 14:30:18 +0100 --- xen/arch/x86/time.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-) diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c index a290aba3e8..84b62f2024 100644 --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -378,7 +378,7 @@ static u64 read_hpet_count(void) static int64_t __init init_hpet(struct platform_timesource *pts) { uint64_t hpet_rate, start; - uint32_t count, target; + uint32_t count, target, elapsed; /* * Allow HPET to be setup, but report a frequency of 0 so it's not selected * as a timer source. This is required so it can be used in legacy @@ -451,11 +451,8 @@ static int64_t __init init_hpet(struct platform_timesource *pts) count = hpet_read32(HPET_COUNTER); start = rdtsc_ordered(); - target = count + CALIBRATE_VALUE(hpet_rate); - if ( target < count ) - while ( hpet_read32(HPET_COUNTER) >= count ) - continue; - while ( hpet_read32(HPET_COUNTER) < target ) + target = CALIBRATE_VALUE(hpet_rate); + while ( (elapsed = hpet_read32(HPET_COUNTER) - count) < target ) continue; return (rdtsc_ordered() - start) * CALIBRATE_FRAC; @@ -493,8 +490,8 @@ static u64 read_pmtimer_count(void) static s64 __init init_pmtimer(struct platform_timesource *pts) { - u64 start; - u32 count, target, mask; + uint64_t start; + uint32_t count, target, mask, elapsed; if ( !pmtmr_ioport || (pmtmr_width != 24 && pmtmr_width != 32) ) return 0; @@ -502,13 +499,10 @@ static s64 __init init_pmtimer(struct platform_timesource *pts) pts->counter_bits = pmtmr_width; mask = 0xffffffff >> (32 - pmtmr_width); - count = inl(pmtmr_ioport) & mask; + count = inl(pmtmr_ioport); start = rdtsc_ordered(); - target = count + CALIBRATE_VALUE(ACPI_PM_FREQUENCY); - if ( target < count ) - while ( (inl(pmtmr_ioport) & mask) >= count ) - continue; - while ( (inl(pmtmr_ioport) & mask) < target ) + target = CALIBRATE_VALUE(ACPI_PM_FREQUENCY); + while ( (elapsed = (inl(pmtmr_ioport) - count) & mask) < target ) continue; return (rdtsc_ordered() - start) * CALIBRATE_FRAC; -- 2.30.2