Re: [RFC PATCH 2/3] drm/xe: Log when a timed out TLB invalidation ack finally arrives

On Mon, Aug 03, 2026 at 11:14:40PM -0300, Tales A. Mendonça wrote:
> When a TLB invalidation fence times out we log the timeout, but if the
> ack for that seqno later shows up there is no record of it, making it
> impossible to tell from logs whether the ack was lost forever or merely
> (very) late.
> 
> Track the most recent timed out seqno and log how late its ack arrives,
> relative to both the original request and the moment the fence was
> signaled with -ETIME.
> 
> On ARL with GuC 70.53.0 this shows the acks are never lost: they
> consistently arrive ~2.3s after the request, tens of milliseconds after
> the TDR has already signaled the fence:
> 
>   TLB invalidation fence timeout, seqno=10992 recv=10991
>   TLB invalidation late ack: seqno=10992 recv=10992, request-to-ack=2314ms, timeout-to-ack=45ms
> 
> Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8678
> Signed-off-by: Tales A. Mendonça <[email protected]>
> ---
>  drivers/gpu/drm/xe/xe_tlb_inval.c       | 16 ++++++++++++++++
>  drivers/gpu/drm/xe/xe_tlb_inval_types.h | 17 +++++++++++++++++
>  2 files changed, 33 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_tlb_inval.c b/drivers/gpu/drm/xe/xe_tlb_inval.c
> index 833fb92cd3e..9dd04d5bc4c 100644
> --- a/drivers/gpu/drm/xe/xe_tlb_inval.c
> +++ b/drivers/gpu/drm/xe/xe_tlb_inval.c
> @@ -99,6 +99,9 @@ static void xe_tlb_inval_fence_timeout(struct work_struct *work)
>  			fence->seqno, tlb_inval->seqno_recv);
>  
>  		timedout_seqno = fence->seqno;

Should this be:

if (!tlb_inval->timedout_seqno) {
	tlb_inval->timedout_seqno = fence->seqno;
	tlb_inval->timedout_inval_time = fence->inval_time;
	tlb_inval->timedout_time = ktime_get();
}

To record the very first timeout seqno? I think this makes more sense.

> +		tlb_inval->timedout_seqno = fence->seqno;
> +		tlb_inval->timedout_inval_time = fence->inval_time;
> +		tlb_inval->timedout_time = ktime_get();
>  
>  		fence->base.error = -ETIME;
>  		xe_tlb_inval_fence_signal(fence);
> @@ -227,6 +230,7 @@ void xe_tlb_inval_reset(struct xe_tlb_inval *tlb_inval)
>  	else
>  		pending_seqno = tlb_inval->seqno - 1;
>  	WRITE_ONCE(tlb_inval->seqno_recv, pending_seqno);
> +	tlb_inval->timedout_seqno = 0;
>  
>  	list_for_each_entry_safe(fence, next,
>  				 &tlb_inval->pending_fences, link)
> @@ -424,6 +428,18 @@ void xe_tlb_inval_done_handler(struct xe_tlb_inval *tlb_inval, int seqno)
>  
>  	WRITE_ONCE(tlb_inval->seqno_recv, seqno);
>  
> +	if (tlb_inval->timedout_seqno &&
> +	    xe_tlb_inval_seqno_past(tlb_inval, tlb_inval->timedout_seqno)) {
> +		ktime_t now = ktime_get();
> +
> +		drm_warn(&xe->drm,

I think xe_warn is the preference here.

Matt

> +			 "TLB invalidation late ack: seqno=%d recv=%d, request-to-ack=%lldms, timeout-to-ack=%lldms",
> +			 tlb_inval->timedout_seqno, seqno,
> +			 ktime_ms_delta(now, tlb_inval->timedout_inval_time),
> +			 ktime_ms_delta(now, tlb_inval->timedout_time));
> +		tlb_inval->timedout_seqno = 0;
> +	}
> +
>  	list_for_each_entry_safe(fence, next,
>  				 &tlb_inval->pending_fences, link) {
>  		trace_xe_tlb_inval_fence_recv(xe, fence);
> diff --git a/drivers/gpu/drm/xe/xe_tlb_inval_types.h b/drivers/gpu/drm/xe/xe_tlb_inval_types.h
> index 3d1797d186f..38288966254 100644
> --- a/drivers/gpu/drm/xe/xe_tlb_inval_types.h
> +++ b/drivers/gpu/drm/xe/xe_tlb_inval_types.h
> @@ -102,6 +102,23 @@ struct xe_tlb_inval {
>  	 * @pending_lock: protects @pending_fences and updating @seqno_recv.
>  	 */
>  	spinlock_t pending_lock;
> +	/**
> +	 * @timedout_seqno: seqno of the most recent timed out TLB
> +	 * invalidation, 0 if none. Used to measure how late the ack for a
> +	 * timed out invalidation actually arrives. Protected by
> +	 * @pending_lock.
> +	 */
> +	int timedout_seqno;
> +	/**
> +	 * @timedout_inval_time: request time of @timedout_seqno. Protected by
> +	 * @pending_lock.
> +	 */
> +	ktime_t timedout_inval_time;
> +	/**
> +	 * @timedout_time: time @timedout_seqno was signaled with -ETIME.
> +	 * Protected by @pending_lock.
> +	 */
> +	ktime_t timedout_time;
>  	/**
>  	 * @fence_tdr: schedules a delayed call to xe_tlb_fence_timeout after
>  	 * the timeout interval is over.
> -- 
> 2.55.0
>