Quoting Tvrtko Ursulin (2018-04-24 10:40:57)
>
> On 24/04/2018 10:33, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-04-24 10:27:23)
> >>
> >> On 24/04/2018 09:16, Chris Wilson wrote:
> >>> If we have more than a few, possibly several thousand request in the
> >>> queue, don't show the central portion, just the first few and the last
> >>> being executed and/or queued. The first few should be enough to help
> >>> identify a problem in execution, and most often comparing the first/last
> >>> in the queue is enough to identify problems in the scheduling.
> >>>
> >>> We may need some fine tuning to set MAX_REQUESTS_TO_SHOW for common
> >>> debug scenarios, but for the moment if we can avoiding spending more
> >>> than a few seconds dumping the GPU state that will avoid a nasty
> >>> livelock (where hangcheck spends so long dumping the state, it fires
> >>> again and starts to dump the state again in parallel, ad infinitum).
> >>>
> >>> v2: Remember to print last not the stale rq iter after the loop.
> >>>
> >>> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >>> ---
> >>> drivers/gpu/drm/i915/intel_engine_cs.c | 43 +++++++++++++++++++++++---
> >>> 1 file changed, 38 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> >>> index 66cddd059666..2398ea71e747 100644
> >>> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> >>> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> >>> @@ -1307,11 +1307,13 @@ void intel_engine_dump(struct intel_engine_cs *engine,
> >>> struct drm_printer *m,
> >>> const char *header, ...)
> >>> {
> >>> + const int MAX_REQUESTS_TO_SHOW = 8;
> >>> struct intel_breadcrumbs * const b = &engine->breadcrumbs;
> >>> const struct intel_engine_execlists * const execlists = &engine->execlists;
> >>> struct i915_gpu_error * const error = &engine->i915->gpu_error;
> >>> - struct i915_request *rq;
> >>> + struct i915_request *rq, *last;
> >>> struct rb_node *rb;
> >>> + int count;
> >>>
> >>> if (header) {
> >>> va_list ap;
> >>> @@ -1378,16 +1380,47 @@ void intel_engine_dump(struct intel_engine_cs *engine,
> >>> }
> >>>
> >>> spin_lock_irq(&engine->timeline->lock);
> >>> - list_for_each_entry(rq, &engine->timeline->requests, link)
> >>> - print_request(m, rq, " E ");
> >>> +
> >>> + last = NULL;
> >>> + count = 0;
> >>> + list_for_each_entry(rq, &engine->timeline->requests, link) {
> >>> + if (count++ < MAX_REQUESTS_TO_SHOW - 1)
> >>> + print_request(m, rq, " E ");
> >>> + else
> >>> + last = rq;
> >>
> >> else {
> >> last = list_last_entry(...) ?
> >> break;
> >> }
> >>
> >>> + }
> >>> + if (last) {
> >>> + if (count > MAX_REQUESTS_TO_SHOW) {
> >>> + drm_printf(m,
> >>> + " ...skipping %d executing requests...\n",
> >>> + count - MAX_REQUESTS_TO_SHOW);
> >>> + }
> >>> + print_request(m, last, " E ");
> >>> + }
> >>
> >> Or even stuff this printf in the first loop above, under the else
> >> branch. Maybe shorter would be like this, module off by ones if I made some:
> >>
> >> list_for_each_entry(rq, &engine->timeline->requests, link) {
> >> struct i915_request *pr = rq;
> >>
> >> if (++count > MAX_REQUESTS_TO_SHOW) {
> >> pr = list_last_entry(...);
> >> drm_printf(m,
> >> " ...skipping %d executing requests...\n",
> >> count - MAX_REQUESTS_TO_SHOW);
> >> }
> >>
> >> print_request(m, pr, " E ");
> >>
> >> if (count > MAX_REQUESTS_TO_SHOW)
> >> break;
> >> }
> >>
> >>> +
> >>> + last = NULL;
> >>> + count = 0;
> >>> drm_printf(m, " Queue priority: %d\n", execlists->queue_priority);
> >>> for (rb = execlists->first; rb; rb = rb_next(rb)) {
> >>> struct i915_priolist *p =
> >>> rb_entry(rb, typeof(*p), node);
> >>>
> >>> - list_for_each_entry(rq, &p->requests, sched.link)
> >>> - print_request(m, rq, " Q ");
> >>> + list_for_each_entry(rq, &p->requests, sched.link) {
> >>> + if (count++ < MAX_REQUESTS_TO_SHOW - 1)
> >>> + print_request(m, rq, " Q ");
> >>> + else
> >>> + last = rq;
> >>> + }
> >>> }
> >>> + if (last) {
> >>> + if (count > MAX_REQUESTS_TO_SHOW) {
> >>> + drm_printf(m,
> >>> + " ...skipping %d queued requests...\n",
> >>> + count - MAX_REQUESTS_TO_SHOW);
> >>> + }
> >>> + print_request(m, last, " Q ");
> >>> + }
> >>
> >> Then I am thinking how to avoid the duplication and extract the smart
> >> printer. Macro would be easy at least, if a bit ugly.
> >
> > Yeah, and for the moment, I'd like to keep the duplication obvious and
> > keep the two passes very similar.
> >
> >> Another idea comes to mind, but probably for the future, to merge same
> >> prio, context and strictly consecutive seqnos to a single line of output
> >> like:
> >>
> >> [prefix]seqno-seqno [%llx:seqno-seqno] (%u consecutive requests)
> >>
> >> Give or take, but it will be more involved to do that.
> >
> > Deciding when rq are equivalent will get messy, and going to drift.
> >
> >>
> >>> +
> >>> spin_unlock_irq(&engine->timeline->lock);
> >>>
> >>> spin_lock_irq(&b->rb_lock);
> >>>
> >>
> >> Looks OK in general, just please see if you like my idea to contain the
> >> logic within a single loop and maybe even move it to a macro.
> >
> > I don't, because it missed one important thing, the count of skipped
> > requests. :-p
>
> Doh.. Well, I don't like it, but have no better/easier ideas at the moment.
>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
I'll take it as an improvement that can be refined again and again and
again...
Thanks,
-Chris
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