On 06/01/2022 18:33, Teres Alexis, Alan Previn wrote:
On Thu, 2022-01-06 at 09:38 +0000, Tvrtko Ursulin wrote:
On 05/01/2022 17:30, Teres Alexis, Alan Previn wrote:
On Tue, 2022-01-04 at 13:56 +0000, Tvrtko Ursulin wrote:
The flow of events are as below:
1. guc sends notification that an error capture was done and ready to take.
- at this point we copy the guc error captured dump into an interim store
(larger buffer that can hold multiple captures).
2. guc sends notification that a context was reset (after the prior)
- this triggers a call to i915_gpu_coredump with the corresponding engine-mask
from the context that was reset
- i915_gpu_coredump proceeds to gather entire gpu state including driver state,
global gpu state, engine state, context vmas and also engine registers. For the
engine registers now call into the guc_capture code which merely needs to verify
that GuC had already done a step 1 and we have data ready to be parsed.
What about the time between the actual reset and receiving the context
reset notification? Latter will contain intel_context->guc_id - can that
be re-assigned or "retired" in between the two and so cause problems for
matching the correct (or any) vmas?
Not it cannot because its only after the context reset notification that i915 starts
taking action against that cotnext - and even that happens after the i915_gpu_codedump (engine-mask-of-context) happens.
That's what i've observed in the code flow.
The fact it is "only after" is exactly why I asked.
Reset notification is in a CT queue with other stuff, right? So can be
some unrelated time after the actual reset. Could have context be
retired in the meantime and guc_id released is the question.
Because i915 has no idea there was a reset until this delayed message
comes over, but it could see user interrupt signaling end of batch,
after the reset has happened, unbeknown to i915, right?
Perhaps the answer is guc_id cannot be released via the request retire
flows. Or GuC signaling release of guc_id is a thing, which is then
ordered via the same CT buffer.
I don't know, just asking.
As long as the context is pinned, the guc-id wont be re-assigned. After a bit of offline brain-dump
from John Harrison, there are many factors that can keep the context pinned (recounts) including
new or oustanding requests. So a guc-id can't get re-assigned between a capture-notify and a
context-reset even if that outstanding request is the only refcount left since it would still
be considered outstanding by the driver. I also think we may also be talking past each other
in the sense that the guc-id is something the driver assigns to a context being pinned and only
the driver can un-assign it (both assigning and unasigning is via H2G interactions).
I get the sense you are assuming the GuC can un-assign the guc-id's on its own - which isn't
the case. Apologies if i mis-assumed.
I did not think GuC can re-assign ce->guc_id. I asked about request/context complete/retire happening before reset/capture notification is received.
That would be the time window between the last intel_context_put, so last i915_request_put from retire, at which point AFAICT GuC code releases the guc_id. Execution timeline like:
|------ rq1 ------|------ rq2 ------|
^ engine reset ^ rq2, rq1 retire, guc id released
^ GuC reset notify received - guc_id not known any more?
You are saying something is guaranteed to be holding onto the guc_id at the point of receiving the notification? "There are many factors that can keep the context pinned" - what is it in this case? Or the case cannot happen?
Regards,
Tvrtko
