On Wed, 15 Oct 2025 17:03:51 -0700, Umesh Nerlige Ramappa wrote: > > When tick values are large, the multiplication by NSEC_PER_SEC is larger > than 64 bits and results in bad conversions. > > The issue is seen in PMU busyness counters that look like they have > wrapped around due to bad conversion. i915 PMU implementation returns > monotonically increasing counters. If a count is lesser than previous > one, it will only return the larger value until the smaller value > catches up. The user will see this as zero delta between two > measurements even though the engines are busy. > > Fix it by using mul_u64_u32_div()
Reviewed-by: Ashutosh Dixit <[email protected]> > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14955 > Signed-off-by: Umesh Nerlige Ramappa <[email protected]> > --- > v2: > - Fix divide by zero for Gen11 (Andi) > - Update commit message > > v3: > - Drop GCD and use mul_u64_u32_div() instead (Ashutosh) > --- > drivers/gpu/drm/i915/gt/intel_gt_clock_utils.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_clock_utils.c > b/drivers/gpu/drm/i915/gt/intel_gt_clock_utils.c > index 88b147fa5cb1..c90b35881a26 100644 > --- a/drivers/gpu/drm/i915/gt/intel_gt_clock_utils.c > +++ b/drivers/gpu/drm/i915/gt/intel_gt_clock_utils.c > @@ -205,7 +205,7 @@ static u64 div_u64_roundup(u64 nom, u32 den) > > u64 intel_gt_clock_interval_to_ns(const struct intel_gt *gt, u64 count) > { > - return div_u64_roundup(count * NSEC_PER_SEC, gt->clock_frequency); > + return mul_u64_u32_div(count, NSEC_PER_SEC, gt->clock_frequency); > } > > u64 intel_gt_pm_interval_to_ns(const struct intel_gt *gt, u64 count) > @@ -215,7 +215,7 @@ u64 intel_gt_pm_interval_to_ns(const struct intel_gt *gt, > u64 count) > > u64 intel_gt_ns_to_clock_interval(const struct intel_gt *gt, u64 ns) > { > - return div_u64_roundup(gt->clock_frequency * ns, NSEC_PER_SEC); > + return mul_u64_u32_div(ns, gt->clock_frequency, NSEC_PER_SEC); > } > > u64 intel_gt_ns_to_pm_interval(const struct intel_gt *gt, u64 ns) > -- > 2.43.0 >
