Re: [Intel-gfx] [PATCH] drm/i915/gt: Switch to manual evaluation of RPS

[Andi Shyti <andi@etezian.org>]

Hi Chris,

On Sat, Apr 25, 2020 at 07:54:00PM +0100, Chris Wilson wrote:
> As with the realisation for soft-rc6, we respond to idling the engines
> within microseconds, far faster than the response times for HW RC6 and
> RPS. Furthermore, our fast parking upon idle, prevents HW RPS from
> running for many desktop workloads, as the RPS evaluation intervals are
> on the order of tens of milliseconds, but the typical workload is just a
> couple of milliseconds, but yet we still need to determine the best
> frequency for user latency versus power.
> 
> Recognising that the HW evaluation intervals are a poor fit, and that
> they were deprecated [in bspec at least] from gen10, start to wean
> ourselves off them and replace the EI with a timer and our accurate
> busy-stats. The principle benefit of manually evaluating RPS intervals
> is that we can be more responsive for better performance and powersaving
> for both spiky workloads and steady-state.

basically, when you unpark, you wait a bit depending on the
workload before actually setting the rps and you do this by
creating a timer.

> +static bool has_busy_stats(struct intel_rps *rps)
> +{
> +	struct intel_engine_cs *engine;
> +	enum intel_engine_id id;
> +
> +	return HAS_EXECLISTS(rps_to_i915(rps)); /* XXX init ordering */
> +
> +	for_each_engine(engine, rps_to_gt(rps), id) {
> +		if (!intel_engine_supports_stats(engine))
> +			return false;
> +	}
> +
> +	return true;
> +}

mh? what's the exit point here?

Andi
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