Re: [PATCH v2 3/6] drm/xe/guc: Limit sleep while waiting for H2G credits

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Jan 27, 2026 at 08:37:23PM +0100, Michal Wajdeczko wrote:
> Instead of endlessly increasing the sleep timeout while waiting
> for the H2G credits, use exponential increase only up to the given
> limit, like it was initially done in the GuC submission code.
> 
> While here, fix the actual timeout to the 1s as it was documented.

Yes, the existing wait is 2s which seems to be overkill.

> 
> Suggested-by: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_guc_ct.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> index dfbf76037b04..d4111124cd5f 100644
> --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> @@ -32,6 +32,7 @@
>  #include "xe_guc_tlb_inval.h"
>  #include "xe_map.h"
>  #include "xe_pm.h"
> +#include "xe_sleep.h"
>  #include "xe_sriov_vf.h"
>  #include "xe_trace_guc.h"
>  
> @@ -1101,7 +1102,8 @@ static int dequeue_one_g2h(struct xe_guc_ct *ct);
>   */
>  static bool guc_ct_send_wait_for_retry(struct xe_guc_ct *ct, u32 len,
>  				       u32 g2h_len, struct g2h_fence *g2h_fence,
> -				       unsigned int *sleep_period_ms)
> +				       unsigned int *sleep_period_ms,
> +				       unsigned int *sleep_total_ms)
>  {
>  	struct xe_device *xe = ct_to_xe(ct);
>  
> @@ -1115,15 +1117,14 @@ static bool guc_ct_send_wait_for_retry(struct xe_guc_ct *ct, u32 len,
>  	if (!h2g_has_room(ct, len + GUC_CTB_HDR_LEN)) {
>  		struct guc_ctb *h2g = &ct->ctbs.h2g;
>  
> -		if (*sleep_period_ms == 1024)
> +		if (*sleep_total_ms > 1000)
>  			return false;
>  
>  		trace_xe_guc_ct_h2g_flow_control(xe, h2g->info.head, h2g->info.tail,
>  						 h2g->info.size,
>  						 h2g->info.space,
>  						 len + GUC_CTB_HDR_LEN);
> -		msleep(*sleep_period_ms);
> -		*sleep_period_ms <<= 1;
> +		xe_sleep_exponential_ms(sleep_period_ms, 64);
>  	} else {
>  		struct xe_device *xe = ct_to_xe(ct);
>  		struct guc_ctb *g2h = &ct->ctbs.g2h;
> @@ -1161,6 +1162,7 @@ static int guc_ct_send_locked(struct xe_guc_ct *ct, const u32 *action, u32 len,
>  {
>  	struct xe_gt *gt = ct_to_gt(ct);
>  	unsigned int sleep_period_ms = 1;
> +	unsigned int sleep_total_ms = 0;
>  	int ret;
>  
>  	xe_gt_assert(gt, !g2h_len || !g2h_fence);
> @@ -1173,7 +1175,7 @@ static int guc_ct_send_locked(struct xe_guc_ct *ct, const u32 *action, u32 len,
>  
>  	if (unlikely(ret == -EBUSY)) {
>  		if (!guc_ct_send_wait_for_retry(ct, len, g2h_len, g2h_fence,
> -						&sleep_period_ms))
> +						&sleep_period_ms, &sleep_total_ms))
>  			goto broken;
>  		goto try_again;
>  	}
> -- 
> 2.47.1
>