Quoting Chris Wilson (2017-11-20 16:45:44) > Quoting Michel Thierry (2017-11-20 16:17:01) > > On 11/20/2017 4:34 AM, Chris Wilson wrote: > > > The hardware needs some time to process the information received in the > > > ExecList Submission Port, and expects us to not write anything more until > > > it has 'acknowledged' this new submission by sending an IDLE_ACTIVE or > > > PREEMPTED CSB event. > > > > > > If we do not follow this, the driver could write new data into the ELSP > > > before HW had finishing fetching the previous one, putting us in > > > 'undefined behaviour' space. > > > > > > This seems to be the problem causing the spurious PREEMPTED & COMPLETE > > > events after a COMPLETE like the one below: > > > > > > [] vcs0: sw rd pointer = 2, hw wr pointer = 0, current 'head' = 3. > > > [] vcs0: Execlist CSB[0]: 0x00000018 _ 0x00000007 > > > [] vcs0: Execlist CSB[1]: 0x00000001 _ 0x00000000 > > > [] vcs0: Execlist CSB[2]: 0x00000018 _ 0x00000007 <<< COMPLETE > > > [] vcs0: Execlist CSB[3]: 0x00000012 _ 0x00000007 <<< PREEMPTED & COMPLETE > > > [] vcs0: Execlist CSB[4]: 0x00008002 _ 0x00000006 > > > [] vcs0: Execlist CSB[5]: 0x00000014 _ 0x00000006 > > > > > > The ELSP writes that lead to this CSB sequence show that the HW hadn't > > > started executing the previous execlist (the one with only ctx 0x6) by the > > > time the new one was submitted; this is a bit more clear in the data > > > show in the EXECLIST_STATUS register at the time of the ELSP write. > > > > > > [] vcs0: ELSP[0] = 0x0_0 [execlist1] - status_reg = 0x0_302 > > > [] vcs0: ELSP[1] = 0x6_fedb2119 [execlist0] - status_reg = 0x0_8302 > > > > > > [] vcs0: ELSP[2] = 0x7_fedaf119 [execlist1] - status_reg = 0x0_8308 > > > [] vcs0: ELSP[3] = 0x6_fedb2119 [execlist0] - status_reg = 0x7_8308 > > > > > > Note that having to wait for this ack does not disable lite-restores, > > > although it may reduce their numbers. > > > > > > v2: Rewrote Michel's patch, his digging and his fix, my spelling. > > > v3: Reorder to ack early to allow preemption > > > > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102035 > > > Suggested-by: Michel Thierry <michel.thierry@xxxxxxxxx> > > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > > Cc: Michel Thierry <michel.thierry@xxxxxxxxx> > > > > Isn't it nice to come back after the weekend and see everything is ok? > > > > Reviewed-by: Michel Thierry <michel.thierry@xxxxxxxxx> > > Do you want to do a quick review-author swap? You take authorship and > I'll take reviewership? It is basically your patch. :) Michel said, on irc, that he didn't mind who took authorship, so I gave it back to him for doing the work, and pushed. Thanks for the really nasty bug fix, -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
