On Wed, Apr 20, 2016 at 04:43:56PM +0300, ville.syrjala@xxxxxxxxxxxxxxx wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> Somehow my SNB GT1 (Dell XPS 8300) gets very unhappy around
> GPU hangs if the RPS EI/thresholds aren't suitably aligned.
> It seems like scheduling/timer interupts stop working somehow
> and things get stuck eg. in usleep_range().
>
> I bisected the problem down to
> commit 8a5864377b12 ("drm/i915/skl: Restructured the gen6_set_rps_thresholds function")
> I observed that before all the values were at least multiples of 25,
> but afterwards they are not. And rounding things up to the next multiple
> of 25 does seem to help, so lets' do that. I also tried roundup(..., 5)
> but that wasn't sufficient. Also I have no idea if we might need this sort of
> thing on gen9+ as well.
Do we need to test for performance regressions on stuff like this? And if so,
who do we ping about this?
OTOH impact should be really small and since this fixes a real problem:
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@xxxxxxxxxxxxxxx>
>
> These are the original EI/thresholds:
> LOW_POWER
> GEN6_RP_UP_EI 12500
> GEN6_RP_UP_THRESHOLD 11800
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 21250
> BETWEEN
> GEN6_RP_UP_EI 10250
> GEN6_RP_UP_THRESHOLD 9225
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 18750
> HIGH_POWER
> GEN6_RP_UP_EI 8000
> GEN6_RP_UP_THRESHOLD 6800
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 15000
>
> These are after 8a5864377b12:
> LOW_POWER
> GEN6_RP_UP_EI 12500
> GEN6_RP_UP_THRESHOLD 11875
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 21250
> BETWEEN
> GEN6_RP_UP_EI 10156
> GEN6_RP_UP_THRESHOLD 9140
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 18750
> HIGH_POWER
> GEN6_RP_UP_EI 7812
> GEN6_RP_UP_THRESHOLD 6640
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 15000
>
> And these are what we have after this patch:
> LOW_POWER
> GEN6_RP_UP_EI 12500
> GEN6_RP_UP_THRESHOLD 11875
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 21250
> BETWEEN
> GEN6_RP_UP_EI 10175
> GEN6_RP_UP_THRESHOLD 9150
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 18750
> HIGH_POWER
> GEN6_RP_UP_EI 7825
> GEN6_RP_UP_THRESHOLD 6650
> GEN6_RP_DOWN_EI 25000
> GEN6_RP_DOWN_THRESHOLD 15000
>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Akash Goel <akash.goel@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Testcase: igt/kms_pipe_crc_basic/hang-read-crc-pipe-B
> Fixes: 8a5864377b12 ("drm/i915/skl: Restructured the gen6_set_rps_thresholds function")
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_reg.h | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index c21b71c86a6b..08f01f4470cd 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -2948,7 +2948,14 @@ enum skl_disp_power_wells {
> #define GEN6_RP_STATE_CAP _MMIO(MCHBAR_MIRROR_BASE_SNB + 0x5998)
> #define BXT_RP_STATE_CAP _MMIO(0x138170)
>
> -#define INTERVAL_1_28_US(us) (((us) * 100) >> 7)
> +/*
> + * Make these a multiple of magic 25 to avoid SNB (eg. Dell XPS
> + * 8300) freezing up around GPU hangs. Looks as if even
> + * scheduling/timer interrupts start misbehaving if the RPS
> + * EI/thresholds are "bad", leading to a very sluggish or even
> + * frozen machine.
> + */
> +#define INTERVAL_1_28_US(us) roundup(((us) * 100) >> 7, 25)
> #define INTERVAL_1_33_US(us) (((us) * 3) >> 2)
> #define INTERVAL_0_833_US(us) (((us) * 6) / 5)
> #define GT_INTERVAL_FROM_US(dev_priv, us) (IS_GEN9(dev_priv) ? \
> --
> 2.7.4
>
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