[Intel-gfx] [PATCH v4] drm/i915: Flush the ring stop bit after clearing RING_HEAD in reset
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Fri May 25 08:36:18 UTC 2018
On 24/05/2018 14:40, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2018-05-24 14:34:41)
>>
>> On 19/05/2018 10:04, Chris Wilson wrote:
>>> Quoting Tvrtko Ursulin (2018-05-18 15:42:00)
>>>>
>>>> On 18/05/2018 15:13, Chris Wilson wrote:
>>>>> Quoting Tvrtko Ursulin (2018-05-18 13:36:52)
>>>>>>
>>>>>> On 18/05/2018 13:28, Chris Wilson wrote:
>>>>>>> Quoting Tvrtko Ursulin (2018-05-18 12:50:41)
>>>>>>>>
>>>>>>>> On 18/05/2018 12:10, Chris Wilson wrote:
>>>>>>>>> Quoting Tvrtko Ursulin (2018-05-18 12:05:17)
>>>>>>>>>>
>>>>>>>>>> On 18/05/2018 11:09, Chris Wilson wrote:
>>>>>>>>>>> Inside the live_hangcheck (reset) selftests, we occasionally see
>>>>>>>>>>> failures like
>>>>>>>>>>>
>>>>>>>>>>> <7>[ 239.094840] i915_gem_set_wedged rcs0
>>>>>>>>>>> <7>[ 239.094843] i915_gem_set_wedged current seqno 19a98, last 19a9a, hangcheck 0 [5158 ms]
>>>>>>>>>>> <7>[ 239.094846] i915_gem_set_wedged Reset count: 6239 (global 1)
>>>>>>>>>>> <7>[ 239.094848] i915_gem_set_wedged Requests:
>>>>>>>>>>> <7>[ 239.095052] i915_gem_set_wedged first 19a99 [e8c:5f] prio=1024 @ 5159ms: (null)
>>>>>>>>>>> <7>[ 239.095056] i915_gem_set_wedged last 19a9a [e81:1a] prio=139 @ 5159ms: igt/rcs0[5977]/1
>>>>>>>>>>> <7>[ 239.095059] i915_gem_set_wedged active 19a99 [e8c:5f] prio=1024 @ 5159ms: (null)
>>>>>>>>>>> <7>[ 239.095062] i915_gem_set_wedged [head 0220, postfix 0280, tail 02a8, batch 0xffffffff_ffffffff]
>>>>>>>>>>> <7>[ 239.100050] i915_gem_set_wedged ring->start: 0x00283000
>>>>>>>>>>> <7>[ 239.100053] i915_gem_set_wedged ring->head: 0x000001f8
>>>>>>>>>>> <7>[ 239.100055] i915_gem_set_wedged ring->tail: 0x000002a8
>>>>>>>>>>> <7>[ 239.100057] i915_gem_set_wedged ring->emit: 0x000002a8
>>>>>>>>>>> <7>[ 239.100059] i915_gem_set_wedged ring->space: 0x00000f10
>>>>>>>>>>> <7>[ 239.100085] i915_gem_set_wedged RING_START: 0x00283000
>>>>>>>>>>> <7>[ 239.100088] i915_gem_set_wedged RING_HEAD: 0x00000260
>>>>>>>>>>> <7>[ 239.100091] i915_gem_set_wedged RING_TAIL: 0x000002a8
>>>>>>>>>>> <7>[ 239.100094] i915_gem_set_wedged RING_CTL: 0x00000001
>>>>>>>>>>> <7>[ 239.100097] i915_gem_set_wedged RING_MODE: 0x00000300 [idle]
>>>>>>>>>>> <7>[ 239.100100] i915_gem_set_wedged RING_IMR: fffffefe
>>>>>>>>>>> <7>[ 239.100104] i915_gem_set_wedged ACTHD: 0x00000000_0000609c
>>>>>>>>>>> <7>[ 239.100108] i915_gem_set_wedged BBADDR: 0x00000000_0000609d
>>>>>>>>>>> <7>[ 239.100111] i915_gem_set_wedged DMA_FADDR: 0x00000000_00283260
>>>>>>>>>>> <7>[ 239.100114] i915_gem_set_wedged IPEIR: 0x00000000
>>>>>>>>>>> <7>[ 239.100117] i915_gem_set_wedged IPEHR: 0x02800000
>>>>>>>>>>> <7>[ 239.100120] i915_gem_set_wedged Execlist status: 0x00044052 00000002
>>>>>>>>>>> <7>[ 239.100124] i915_gem_set_wedged Execlist CSB read 5 [5 cached], write 5 [5 from hws], interrupt posted? no, tasklet queued? no (enabled)
>>>>>>>>>>> <7>[ 239.100128] i915_gem_set_wedged ELSP[0] count=1, ring->start=00283000, rq: 19a99 [e8c:5f] prio=1024 @ 5164ms: (null)
>>>>>>>>>>> <7>[ 239.100132] i915_gem_set_wedged ELSP[1] count=1, ring->start=00257000, rq: 19a9a [e81:1a] prio=139 @ 5164ms: igt/rcs0[5977]/1
>>>>>>>>>>> <7>[ 239.100135] i915_gem_set_wedged HW active? 0x5
>>>>>>>>>>> <7>[ 239.100250] i915_gem_set_wedged E 19a99 [e8c:5f] prio=1024 @ 5164ms: (null)
>>>>>>>>>>> <7>[ 239.100338] i915_gem_set_wedged E 19a9a [e81:1a] prio=139 @ 5164ms: igt/rcs0[5977]/1
>>>>>>>>>>> <7>[ 239.100340] i915_gem_set_wedged Queue priority: 139
>>>>>>>>>>> <7>[ 239.100343] i915_gem_set_wedged Q 0 [e98:19] prio=132 @ 5164ms: igt/rcs0[5977]/8
>>>>>>>>>>> <7>[ 239.100346] i915_gem_set_wedged Q 0 [e84:19] prio=121 @ 5165ms: igt/rcs0[5977]/2
>>>>>>>>>>> <7>[ 239.100349] i915_gem_set_wedged Q 0 [e87:19] prio=82 @ 5165ms: igt/rcs0[5977]/3
>>>>>>>>>>> <7>[ 239.100352] i915_gem_set_wedged Q 0 [e84:1a] prio=44 @ 5164ms: igt/rcs0[5977]/2
>>>>>>>>>>> <7>[ 239.100356] i915_gem_set_wedged Q 0 [e8b:19] prio=20 @ 5165ms: igt/rcs0[5977]/4
>>>>>>>>>>> <7>[ 239.100362] i915_gem_set_wedged drv_selftest [5894] waiting for 19a99
>>>>>>>>>>>
>>>>>>>>>>> where the GPU saw an arbitration point and idles; AND HAS NOT BEEN RESET!
>>>>>>>>>>> The RING_MODE indicates that is idle and has the STOP_RING bit set, so
>>>>>>>>>>> try clearing it.
>>>>>>>>>>>
>>>>>>>>>>> v2: Only clear the bit on restarting the ring, as we want to be sure the
>>>>>>>>>>> STOP_RING bit is kept if reset fails on wedging.
>>>>>>>>>>> v3: Spot when the ring state doesn't make sense when re-initialising the
>>>>>>>>>>> engine and dump it to the logs so that we don't have to wait for an
>>>>>>>>>>> error later and try to guess what happened earlier.
>>>>>>>>>>> v4: Prepare to print all the unexpected state, not just the first.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>>>>>>>>>>> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
>>>>>>>>>>> ---
>>>>>>>>>>> drivers/gpu/drm/i915/intel_lrc.c | 22 ++++++++++++++++++++++
>>>>>>>>>>> 1 file changed, 22 insertions(+)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>>>>>> index 3744f5750624..ba8411ba4abf 100644
>>>>>>>>>>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>>>>>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>>>>>>>>>>> @@ -1781,6 +1781,9 @@ static void enable_execlists(struct intel_engine_cs *engine)
>>>>>>>>>>> I915_WRITE(RING_MODE_GEN7(engine),
>>>>>>>>>>> _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE));
>>>>>>>>>>>
>>>>>>>>>>> + I915_WRITE(RING_MI_MODE(engine->mmio_base),
>>>>>>>>>>> + _MASKED_BIT_DISABLE(STOP_RING));
>>>>>>>>>>
>>>>>>>>>> Worries me a bit to clear it unconditionally since documentation says
>>>>>>>>>> nothing (that I can find) about this scenario.
>>>>>>>>>>
>>>>>>>>>>> +
>>>>>>>>>>> I915_WRITE(RING_HWS_PGA(engine->mmio_base),
>>>>>>>>>>> engine->status_page.ggtt_offset);
>>>>>>>>>>> POSTING_READ(RING_HWS_PGA(engine->mmio_base));
>>>>>>>>>>> @@ -1789,6 +1792,19 @@ static void enable_execlists(struct intel_engine_cs *engine)
>>>>>>>>>>> engine->execlists.csb_head = -1;
>>>>>>>>>>> }
>>>>>>>>>>>
>>>>>>>>>>> +static bool unexpected_starting_state(struct intel_engine_cs *engine)
>>>>>>>>>>> +{
>>>>>>>>>>> + struct drm_i915_private *dev_priv = engine->i915;
>>>>>>>>>>> + bool unexpected = false;
>>>>>>>>>>> +
>>>>>>>>>>> + if (I915_READ(RING_MI_MODE(engine->mmio_base)) & STOP_RING) {
>>>>>>>>>>> + DRM_DEBUG_DRIVER("STOP_RING still set in RING_MI_MODE\n");
>>>>>>>>>>
>>>>>>>>>> Also worries me to bury this as a debug message unless we can find in
>>>>>>>>>> documentation that this is known to happen occasionally.
>>>>>>>>>>
>>>>>>>>>> If we had the check and logging immediately after reset, with a more
>>>>>>>>>> visible log, we could build a larger data set of reported failures and
>>>>>>>>>> then go back to hw people and ask them about it.
>>>>>>>>>
>>>>>>>>> The problem with the reset side is trying to avoid mixing in the case
>>>>>>>>> where we are faking it and expect it to still be set. On the ringbuffer
>>>>>>>>> path, we handle STOP_RING as being part of the init sequence. The log
>>>>>>>>> already says we did a reset and STOP_RING is set (since we have tracing
>>>>>>>>> through the reset), I just need to find the right spot to handle it.
>>>>>>>>
>>>>>>>> The "distance" in code paths between reset and init_hw is probably the
>>>>>>>> smallest of my concerns. If we could make this message not debug only,
>>>>>>>> and clear STOP_RING only conditionally I think I would be happy with
>>>>>>>> giving this a go and see if it collects any data.
>>>>>>>
>>>>>>> Why? Who else but us are going to read it, and why bother if it is not
>>>>>>> actionable. It is logged (was logged already, now highlighted) and for
>>>>>>> the user none of it is relevant, the only thing that matters to them is
>>>>>>> that they don't even notice the system suffered a GPU hang.
>>>>>>
>>>>>> My reasoning is this - something has happened which is completely
>>>>>> unexpected and may have other negative effect which are currently
>>>>>> unknown to us. By logging it at a higher level we collect this now very
>>>>>> specific signature on a wider collection of platforms and can then act
>>>>>> on the collected data set. Also very specific log message makes bug
>>>>>> triage easier and a lower chance it gets bunched up with other hang reports.
>>>>>
>>>>> You do have a very specific debug message, but having a flip-flopping
>>>>> test that has no impact on system stability (as evidenced by the lack of
>>>>> errors, if there was a subsequent error it is imperative that the post
>>>>> mortem capture does its best, everything else is lost) does not help us.
>>>>
>>>> What if we deploy this as DRM_NOTICE/INFO, get reports from the field
>>>> and not just the selftest, and then realize the issue is actually
>>>> interesting and could be fed back to HW design?
>>>
>>> But we already have enough to point out that the HW is not behaving as
>>> we^W I would expect.
>>>
>>> For field analysis, I strongly believe that unless you can capture
>>> everything you need without user intervention, you will never get the
>>> debug information required. The instructions we have are "oops,
>>> something went wrong, please file a new bug report here and attach this
>>> file". That's already too complicated wants to be automated, e.g. abrtd.
>>> But for whatever reason we don't get the reports from abrtd.
>>>
>>> Elsewhere we use the method of light periodic checks and if they spot an
>>> issue, switch on heavy debug mode. For something like this where we want
>>> a trace of operations as they happen? I think we need to be able to turn
>>> on GEM tracing on the fly and be able to capture the compressed buffers.
>>
>> Not sure that we need a trace of pre-events for this. It seems pretty
>> straight-forward to me. Register is not in the state in which it should
>> be immediately after reset.
>
> But you don't always have a reset, that makes throwing a tantrum here
> difficult.
>
>> It will help sort the hang reports into a new bucket.
>
> The information is already in the hang report. What isn't which would be
> useful is the trace of events that precede certain hangs (ones that I
> suspect are driver bugs as opposed to userspace GPU programming issues).
It is there but takes more skill to triage.
Okay, given that the check is not only after reset, and given how you do
a lion's share of bug triaging anyway:
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Regards,
Tvrtko
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