[PATCH] lib/xe/xe_spin: Add additional MI_ARB_CHECK to preemptable spin init

[Matthew Brost]

On Thu, Aug 14, 2025 at 06:50:10PM +0000, Jonathan Cavitt wrote:
> Add an additional MI_ARB_CHECK to the spin initialization function,
> just before the conditional batch buffer end, when preemption is
> enabled.  The MI_ARB_CHECK forces a preemption in this case, which can
> allow additionally scheduled exec queues to make independent progress
> earlier than if we relied on the automatic timeout of the exec queue.
> 
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5783
> Suggested-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
> ---
>  lib/xe/xe_spin.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/xe/xe_spin.c b/lib/xe/xe_spin.c
> index 25f7555e27..b3a937fe80 100644
> --- a/lib/xe/xe_spin.c
> +++ b/lib/xe/xe_spin.c
> @@ -30,7 +30,6 @@
>  
>  enum { START_TS, NOW_TS };
>  
> -
>  uint32_t xe_spin_nsec_to_ticks(int fd, int gt_id, uint64_t nsec)
>  {
>  	uint32_t ticks = xe_nsec_to_ticks(fd, gt_id, nsec);
> @@ -167,6 +166,9 @@ void xe_spin_init(struct xe_spin *spin, struct xe_spin_opts *opts)
>  				   opts->mem_copy->dst->mocs_index;
>  	}
>  
> +	if (opts->preempt)
> +		spin->batch[b++] = MI_ARB_CHECK;

But we already have one these at the top of the loop:

 72         loop_addr = opts->addr + b * sizeof(uint32_t);
 73
 74         spin->batch[b++] = MI_STORE_DWORD_IMM_GEN4;
 75         spin->batch[b++] = start_addr;
 76         spin->batch[b++] = start_addr >> 32;
 77         spin->batch[b++] = 0xc0ffee;
 78
 79         if (opts->preempt)
 80                 spin->batch[b++] = MI_ARB_CHECK;

Line 74 is here the ring loop restarts.

Matt

> +
>  	spin->batch[b++] = MI_COND_BATCH_BUFFER_END | MI_DO_COMPARE | 2;
>  	spin->batch[b++] = 0;
>  	spin->batch[b++] = end_addr;
> -- 
> 2.43.0
>