On Thu, Aug 26, 2021 at 03:59:30PM +0200, Thomas Hellström wrote: > On Thu, 2021-08-26 at 14:44 +0200, Daniel Vetter wrote: > > On Thu, Aug 26, 2021 at 12:45:14PM +0200, Thomas Hellström wrote: > > > Pinned contexts, like the migrate contexts need reset after resume > > > since their context image may have been lost. Also the GuC needs to > > > register pinned contexts. > > > > > > Add a list to struct intel_engine_cs where we add all pinned > > > contexts on > > > creation, and traverse that list at resume time to reset the pinned > > > contexts. > > > > > > This fixes the kms_pipe_crc_basic@suspend-read-crc-pipe-a selftest > > > for now, > > > but proper LMEM backup / restore is needed for full suspend > > > functionality. > > > However, note that even with full LMEM backup / restore it may be > > > desirable to keep the reset since backing up the migrate context > > > images > > > must happen using memcpy() after the migrate context has become > > > inactive, > > > and for performance- and other reasons we want to avoid memcpy() > > > from > > > LMEM. > > > > > > Also traverse the list at guc_init_lrc_mapping() calling > > > guc_kernel_context_pin() for the pinned contexts, like is already > > > done > > > for the kernel context. > > > > > > v2: > > > - Don't reset the contexts on each __engine_unpark() but rather at > > > resume time (Chris Wilson). > > > > > > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx> > > > Cc: Matthew Auld <matthew.auld@xxxxxxxxx> > > > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > > > Cc: Brost Matthew <matthew.brost@xxxxxxxxx> > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > > Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx> > > > > I guess it got lost, but I few weeks ago I stumbled over this and > > wondered > > why we're even setting up a separate context or at least why a > > separate vm > > compared to the gt->vm we have already? > > > > Even on chips with bazillions of copy engines the plan is that we > > only > > reserve a single one for kernel migrations, so there's not really a > > need > > for quite this much generality I think. Maybe check with Jon > > Bloomfield on > > this. > > Are you referring to the generality of the migration code itself or to > the generality of using a list in this patch to register multiple > pinned contexts to an engine? > > For the migration code itself, I figured reserving one copy engine for > migration was strictly needed for recoverable page-faults? In the > current version we're not doing that, but just tying a pinned migration > context to the first available copy engine on the gt, to be used when > we don't have a ww context available to pin a separate context using a > random copy engine. Note also the ring size of the migration contexts; > since we're populating the page-tables for each blit, it's not hard to > fill the ring and in the end multiple contexts I guess boils down to > avoiding priority inversion on migration, including blocking high > priority kernel context tasks. > > As for not using the gt->vm, I'm not completely sure if we can do our > special page-table setup on that, Got to defer that question to Chris, > but once Ram's work of supporting 64K LMEM PTEs on that has landed I > guess we could easily reuse the gt->vm if possible and suitable. Just on why we have gt->vm and then also the migration vm. The old mail I typed up on this: https://lore.kernel.org/dri-devel/CAKMK7uG6g+DQQEcjqeA6=Z2ENHogaMuvKERDgKm5jKq3u+a1jQ@xxxxxxxxxxxxxx/ -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
