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> --- 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 fa86b7ab2d99..199cccac8020 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
