Quoting Chris Wilson (2017-11-16 22:11:30) > If we are about to do another context-switch in the near future skip > doing performing a lite-restore now. (Forcing a lite-restore just before > a context-switch effectively doubles the cost of that context-switch, so > long as we can handle the interrupt and resubmit before the GPU powers > down, which under normal conditions is expected.) > > Coincidentally, skipping a lite-restore just before idling also prevents > (not entirely, but the window for occurrence now depends on the next > context completing within the same period and we have already noted that > we can resubmit faster than the GPU can context switch to make this > worthwhile) an issue on bxt/glk where it may become confused in an attempt > to lite-restore an already idle context, after which nothing is quite the > same again. Well only testing will tell... > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102035 > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_lrc.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c > index 5a22bdffd387..5272eb23d98a 100644 > --- a/drivers/gpu/drm/i915/intel_lrc.c > +++ b/drivers/gpu/drm/i915/intel_lrc.c > @@ -584,6 +584,25 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > if (port_count(&port[1])) > goto unlock; > > + /* > + * If we are about to do another context-switch in > + * the near future skip doing performing a lite-restore > + * now. (Forcing a lite-restore just before a > + * context-switch effectively doubles the cost of that > + * context-switch, so long as we can handle the > + * interrupt and resubmit before the GPU powers down, > + * which under normal conditions is expected.) > + * > + * Skipping a lite-restore just before idling also > + * prevents an issue on bxt/glk where it may become > + * confused in an attempt to lite-restore an already > + * idle context, after which nothing is quite the same > + * again. > + */ > + if (i915_seqno_passed(intel_engine_get_seqno(engine), > + last->global_seqno - 1)) > + goto unlock; > + > /* WaIdleLiteRestore:bdw,skl > * Apply the wa NOOPs to prevent > * ring:HEAD == req:TAIL as we resubmit the The subtext is that lite-restore are pointless... Not sure I fully agree yet; in most scenarios pointless. The last time I was thinking of only doing the lite-restore iff we were on the last request, otherwise we are just interrupting a request which already has a continuation. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
