[Intel-gfx] [PATCH] drm/i915/selftest: Disable IRQ for timestamp calculation

[Dixit, Ashutosh]

On Tue, 30 Nov 2021 05:20:05 -0800, Anshuman Gupta wrote:
>
> gt_pm selftest calculates engine ticks cycles and wall time
> cycles by delta of respective engine elapsed TIMESTAMP and ktime
> for period of 1000us.
> It compares the engine ticks cycles with wall time cycles.
>
> Disable local cpu interrupt so that interrupt handler does not
> switch out the thread during measure_clocks() and prevent
> miscalculation of engine tick cycles.

Reviewed-by: Ashutosh Dixit <ashutosh.dixit at intel.com>

> v2:
> - nuke preempt_{disable,enable}, as disable_local_irq()
>   disable the preemption. (Chris)
>
> Cc: Chris P Wilson <chris.p.wilson at intel.com>
> Cc: Badal Nilawar <badal.nilawar at intel.com>
> Cc: Ashutosh Dixit <ashutosh.dixit at intel.com>
> Signed-off-by: Anshuman Gupta <anshuman.gupta at intel.com>
> ---
>  drivers/gpu/drm/i915/gt/selftest_gt_pm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_gt_pm.c b/drivers/gpu/drm/i915/gt/selftest_gt_pm.c
> index b9441217ca3d..55c5cdb99f45 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_gt_pm.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_gt_pm.c
> @@ -43,7 +43,7 @@ static void measure_clocks(struct intel_engine_cs *engine,
>	int i;
>
>	for (i = 0; i < 5; i++) {
> -		preempt_disable();
> +		local_irq_disable();
>		cycles[i] = -ENGINE_READ_FW(engine, RING_TIMESTAMP);
>		dt[i] = ktime_get();
>
> @@ -51,7 +51,7 @@ static void measure_clocks(struct intel_engine_cs *engine,
>
>		dt[i] = ktime_sub(ktime_get(), dt[i]);
>		cycles[i] += ENGINE_READ_FW(engine, RING_TIMESTAMP);
> -		preempt_enable();
> +		local_irq_enable();
>	}
>
>	/* Use the median of both cycle/dt; close enough */
> --
> 2.26.2
>