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
-Chris
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