Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: > Our forcewake utilisation is split into categories: automatic and > manual. Around bare register reads, we look up the right forcewake > domain and automatically acquire and release [upon a timer] the > forcewake domain. For other access, where we know we require the > forcewake across a group of register reads, we manually acquire the > forcewake domain and release it at the end. Again, this currently arms > the domain timer for a later release. > > However, looking at some energy utilisation profiles, we have tried to > avoid using forcewake [and rely on the natural wake up to post register > updates] due to that even keep the fw active for a brief period > contributes to a significant power draw [i.e. when the gpu is sleeping > with rc6 at high clocks]. But as it turns out, not posting the writes > immediately also has unintended consequences, such as not reducing the > clocks and so conserving power while busy. > > As a compromise, let us only arm the domain timer for automatic > forcewake usage around bare register access, but immediately release the > forcewake when manually acquired by intel_uncore_forcewake_get/_put. > > The corollary to this is that we may instead have to take forcewake more > often, and so incur a latency penalty in doing so. For Sandybridge this > was significant, and even on the latest machines, taking forcewake at > interrupt frequency is a huge impact. [So we don't do that anymore! > Hopefully, this will spare us from still needing the mitigation of the > timer for steady state execution.] > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> I am not a fan of having explicit put relying on timer, Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_uncore.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c > index a61cb8ca4d50..7d6b9ae7403c 100644 > --- a/drivers/gpu/drm/i915/intel_uncore.c > +++ b/drivers/gpu/drm/i915/intel_uncore.c > @@ -709,7 +709,7 @@ static void __intel_uncore_forcewake_put(struct intel_uncore *uncore, > continue; > } > > - fw_domain_arm_timer(domain); > + uncore->funcs.force_wake_put(uncore, domain->mask); > } > } > > -- > 2.20.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
