[Intel-gfx] [PATCH v12] drm/i915: Extend LRC pinning to cover GPU context writeback

[Nick Hoath]

On 25/01/2016 18:19, Daniel Vetter wrote:
> On Fri, Jan 22, 2016 at 02:25:27PM +0000, Nick Hoath wrote:
>> Use the first retired request on a new context to unpin
>> the old context. This ensures that the hw context remains
>> bound until it has been written back to by the GPU.
>> Now that the context is pinned until later in the request/context
>> lifecycle, it no longer needs to be pinned from context_queue to
>> retire_requests.
>> This fixes an issue with GuC submission where the GPU might not
>> have finished writing back the context before it is unpinned. This
>> results in a GPU hang.
>>
>> v2: Moved the new pin to cover GuC submission (Alex Dai)
>>      Moved the new unpin to request_retire to fix coverage leak
>> v3: Added switch to default context if freeing a still pinned
>>      context just in case the hw was actually still using it
>> v4: Unwrapped context unpin to allow calling without a request
>> v5: Only create a switch to idle context if the ring doesn't
>>      already have a request pending on it (Alex Dai)
>>      Rename unsaved to dirty to avoid double negatives (Dave Gordon)
>>      Changed _no_req postfix to __ prefix for consistency (Dave Gordon)
>>      Split out per engine cleanup from context_free as it
>>      was getting unwieldy
>>      Corrected locking (Dave Gordon)
>> v6: Removed some bikeshedding (Mika Kuoppala)
>>      Added explanation of the GuC hang that this fixes (Daniel Vetter)
>> v7: Removed extra per request pinning from ring reset code (Alex Dai)
>>      Added forced ring unpin/clean in error case in context free (Alex Dai)
>> v8: Renamed lrc specific last_context to lrc_last_context as there
>>      were some reset cases where the codepaths leaked (Mika Kuoppala)
>>      NULL'd last_context in reset case - there was a pointer leak
>>      if someone did reset->close context.
>> v9: Rebase over "Fix context/engine cleanup order"
>> v10: Rebase over nightly, remove WARN_ON which caused the
>>      dependency on dev.
>> v11: Kick BAT rerun
>> v12: Rebase
>>
>> Signed-off-by: Nick Hoath <nicholas.hoath at intel.com>
>> Issue: VIZ-4277
>
> When resending patches, please include everyone who ever commented on this
> in Cc: lines here. It's for the record and helps in assigning blame when
> things inevitably blow up again ;-)

Even when it's just a resend to cause a BAT run for coverage?

> -Daniel
>
>> ---
>>   drivers/gpu/drm/i915/intel_lrc.c | 37 +++++++++++++++----------------------
>>   1 file changed, 15 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
>> index dbf3729..b469817 100644
>> --- a/drivers/gpu/drm/i915/intel_lrc.c
>> +++ b/drivers/gpu/drm/i915/intel_lrc.c
>> @@ -779,10 +779,10 @@ intel_logical_ring_advance_and_submit(struct drm_i915_gem_request *request)
>>   	if (intel_ring_stopped(request->ring))
>>   		return 0;
>>
>> -	if (request->ctx != ring->default_context) {
>> -		if (!request->ctx->engine[ring->id].dirty) {
>> +	if (request->ctx != request->ctx->i915->kernel_context) {
>> +		if (!request->ctx->engine[request->ring->id].dirty) {
>>   			intel_lr_context_pin(request);
>> -			request->ctx->engine[ring->id].dirty = true;
>> +			request->ctx->engine[request->ring->id].dirty = true;
>>   		}
>>   	}
>>
>> @@ -2447,9 +2447,7 @@ intel_lr_context_clean_ring(struct intel_context *ctx,
>>   			    struct drm_i915_gem_object *ctx_obj,
>>   			    struct intel_ringbuffer *ringbuf)
>>   {
>> -	int ret;
>> -
>> -	if (ctx == ring->default_context) {
>> +	if (ctx == ctx->i915->kernel_context) {
>>   		intel_unpin_ringbuffer_obj(ringbuf);
>>   		i915_gem_object_ggtt_unpin(ctx_obj);
>>   	}
>> @@ -2463,13 +2461,10 @@ intel_lr_context_clean_ring(struct intel_context *ctx,
>>   		 * otherwise create a switch to idle request
>>   		 */
>>   		if (list_empty(&ring->request_list)) {
>> -			int ret;
>> -
>> -			ret = i915_gem_request_alloc(
>> +			req = i915_gem_request_alloc(
>>   					ring,
>> -					ring->default_context,
>> -					&req);
>> -			if (!ret)
>> +					NULL);
>> +			if (!IS_ERR(req))
>>   				i915_add_request(req);
>>   			else
>>   				DRM_DEBUG("Failed to ensure context saved");
>> @@ -2479,6 +2474,8 @@ intel_lr_context_clean_ring(struct intel_context *ctx,
>>   					typeof(*req), list);
>>   		}
>>   		if (req) {
>> +			int ret;
>> +
>>   			ret = i915_wait_request(req);
>>   			if (ret != 0) {
>>   				/**
>> @@ -2515,17 +2512,13 @@ void intel_lr_context_free(struct intel_context *ctx)
>>   		struct intel_ringbuffer *ringbuf = ctx->engine[i].ringbuf;
>>   		struct drm_i915_gem_object *ctx_obj = ctx->engine[i].state;
>>
>> -		if (!ctx_obj)
>> -			continue;
>> -
>> -		if (ctx == ctx->i915->kernel_context) {
>> -			intel_unpin_ringbuffer_obj(ringbuf);
>> -			i915_gem_object_ggtt_unpin(ctx_obj);
>> -		}
>> +		if (ctx_obj)
>> +			intel_lr_context_clean_ring(
>> +						ctx,
>> +						ringbuf->ring,
>> +						ctx_obj,
>> +						ringbuf);
>>
>> -		WARN_ON(ctx->engine[i].pin_count);
>> -		intel_ringbuffer_free(ringbuf);
>> -		drm_gem_object_unreference(&ctx_obj->base);
>>   	}
>>   }
>>
>> --
>> 1.9.1
>>
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>