Re: [PATCH 1/4] drm/i915: Flush the switch-to-kernel-context harder for DROP_IDLE

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 07/05/2019 13:11, Chris Wilson wrote:
> To complete the idle worker, we must complete 2 passes of wait-for-idle.
> At the end of the first pass, we queue a switch-to-kernel-context and
> may only idle after waiting for its completion. Speed up the flush_work
> by doing the wait explicitly, which then allows us to remove the
> unbounded loop trying to complete the flush_work in the next patch.
> 
> References: 79ffac8599c4 ("drm/i915: Invert the GEM wakeref hierarchy")
> Testcase: igt/gem_ppgtt/flind-and-close-vma-leak
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 14cd83e9ea8b..f60aed7747e5 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -3901,14 +3901,26 @@ i915_drop_caches_set(void *data, u64 val)
>   
>   	/* No need to check and wait for gpu resets, only libdrm auto-restarts
>   	 * on ioctls on -EAGAIN. */
> -	if (val & (DROP_ACTIVE | DROP_RETIRE | DROP_RESET_SEQNO)) {
> +	if (val & (DROP_ACTIVE | DROP_IDLE | DROP_RETIRE | DROP_RESET_SEQNO)) {
>   		int ret;
>   
>   		ret = mutex_lock_interruptible(&i915->drm.struct_mutex);
>   		if (ret)
>   			return ret;
>   
> -		if (val & DROP_ACTIVE)
> +		/*
> +		 * To finish the flush of the idle_worker, we must complete
> +		 * the switch-to-kernel-context, which requires a double
> +		 * pass through wait_for_idle: first queues the switch,
> +		 * second waits for the switch.
> +		 */
> +		if (ret == 0 && val & (DROP_IDLE | DROP_ACTIVE))
> +			ret = i915_gem_wait_for_idle(i915,
> +						     I915_WAIT_INTERRUPTIBLE |
> +						     I915_WAIT_LOCKED,
> +						     MAX_SCHEDULE_TIMEOUT);
> +
> +		if (ret == 0 && val & DROP_IDLE)
>   			ret = i915_gem_wait_for_idle(i915,
>   						     I915_WAIT_INTERRUPTIBLE |
>   						     I915_WAIT_LOCKED,
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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