[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] x86/time: use relative counts in calibration loops
commit 467191641d2a2fd2e43b3ae7b80399f89d339980 Author: Jan Beulich <jbeulich@xxxxxxxx> AuthorDate: Thu Jan 13 14:30:18 2022 +0100 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Thu Jan 13 14:30:18 2022 +0100 x86/time: use relative counts in calibration loops 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 <roger.pau@xxxxxxxxxx> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> --- 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; -- generated by git-patchbot for /home/xen/git/xen.git#staging
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