Re: [Intel-gfx] [PATCH v4] drm/i915/slpc: Optmize waitboost for SLPC

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Fri, 21 Oct 2022 17:24:52 -0700, Vinay Belgaumkar wrote:
>

Hi Vinay,

> Waitboost (when SLPC is enabled) results in a H2G message. This can result
> in thousands of messages during a stress test and fill up an already full
> CTB. There is no need to request for RP0 if boost_freq and the min softlimit
> are the same.
>
> v2: Add the tracing back, and check requested freq
> in the worker thread (Tvrtko)
> v3: Check requested freq in dec_waiters as well
> v4: Only check min_softlimit against boost_freq. Limit this
> optimization for server parts for now.

Sorry I didn't follow. Why are we saying limit this only to server? This:

		if (slpc->min_freq_softlimit == slpc->boost_freq)
			return;

The condition above should work for client too if it is true? But yes it is
typically true automatically for server but not for client. Is that what
you mean?

>
> Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_rps.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_rps.c b/drivers/gpu/drm/i915/gt/intel_rps.c
> index fc23c562d9b2..32e1f5dde5bb 100644
> --- a/drivers/gpu/drm/i915/gt/intel_rps.c
> +++ b/drivers/gpu/drm/i915/gt/intel_rps.c
> @@ -1016,9 +1016,15 @@ void intel_rps_boost(struct i915_request *rq)
>		if (rps_uses_slpc(rps)) {
>			slpc = rps_to_slpc(rps);
>
> +			if (slpc->min_freq_softlimit == slpc->boost_freq)
> +				return;

nit but is it possible that 'slpc->min_freq_softlimit > slpc->boost_freq'
(looks possible to me from the code though we might not have intended it)?
Then we can change this to:

			if (slpc->min_freq_softlimit >= slpc->boost_freq)
				return;


> +
>			/* Return if old value is non zero */
> -			if (!atomic_fetch_inc(&slpc->num_waiters))
> +			if (!atomic_fetch_inc(&slpc->num_waiters)) {
> +				GT_TRACE(rps_to_gt(rps), "boost fence:%llx:%llx\n",
> +					 rq->fence.context, rq->fence.seqno);

Another possibility would have been to add the trace to slpc_boost_work but
this is matches host turbo so I think it is fine here.

>				schedule_work(&slpc->boost_work);
> +			}
>
>			return;
>		}

Thanks.
--
Ashutosh