Quoting Lis, Tomasz (2018-10-19 19:00:15) > > > On 2018-10-16 12:53, Joonas Lahtinen wrote: > > Quoting Tomasz Lis (2018-10-15 20:29:18) > >> The patch adds support of preempt-to-idle requesting by setting a proper > >> bit within Execlist Control Register, and receiving preemption result from > >> Context Status Buffer. > >> > >> Preemption in previous gens required a special batch buffer to be executed, > >> so the Command Streamer never preempted to idle directly. In Icelake it is > >> possible, as there is a hardware mechanism to inform the kernel about > >> status of the preemption request. > >> > >> This patch does not cover using the new preemption mechanism when GuC is > >> active. > >> > >> v2: Added needs_preempt_context() change so that it is not created when > >> preempt-to-idle is supported. (Chris) > >> Updated setting HWACK flag so that it is cleared after > >> preempt-to-dle. (Chris, Daniele) > >> Updated to use I915_ENGINE_HAS_PREEMPTION flag. (Chris) > >> > >> v3: Fixed needs_preempt_context() change. (Chris) > >> Merged preemption trigger functions to one. (Chris) > >> Fixed conyext state tonot assume COMPLETED_MASK after preemption, > >> since idle-to-idle case will not have it set. > >> > >> v4: Simplified needs_preempt_context() change. (Daniele) > >> Removed clearing HWACK flag in idle-to-idle preempt. (Daniele) > >> > >> v5: Renamed inject_preempt_context(). (Daniele) > >> Removed duplicated GEM_BUG_ON() on HWACK (Daniele) > >> > >> Bspec: 18922 > >> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > >> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > >> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx> > >> Cc: Michal Winiarski <michal.winiarski@xxxxxxxxx> > >> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > >> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx> > > This R-b was on v4, and should be indicated with # v4 comment. > > > > The commit message doesn't say much about why preempting to idle is > > beneficial? The pre-Gen11 codepath needs to be maintained anyway. > > > > Regards, Joonas > The benefit is one less context switch - there is no "preempt context". Yes. But that still doesn't quite explain what material benefits there are? :) Is there some actual workloads/microbenchmarks that get an improvement? This alters the behavior between different platforms for a very delicate feature, probably resulting in slightly different bugs. So there should be some more reasoning than just because we can. Regards, Joonas _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
