Re: [PATCH] drm/xe/guc/tlb: Flush g2h worker in case of tlb timeout

["Nilawar, Badal" <badal.nilawar@intel.com>]

On 23-10-2024 20:43, Nirmoy Das wrote:
> Flush the g2h worker explicitly if TLB timeout happens which is
> observed on LNL and that points recent scheduling issue with E-cores.
> This is similar to the recent fix:
> commit e51527233804 ("drm/xe/guc/ct: Flush g2h worker in case of g2h
> response timeout") and should be removed once there is E core
> scheduling fix.
> 
> Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2687
> Cc: Badal Nilawar <badal.nilawar@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: John Harrison <John.C.Harrison@Intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> index 773de1f08db9..2c327dccbd74 100644
> --- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> +++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> @@ -72,6 +72,15 @@ static void xe_gt_tlb_fence_timeout(struct work_struct *work)
>   	struct xe_device *xe = gt_to_xe(gt);
>   	struct xe_gt_tlb_invalidation_fence *fence, *next;
>   
> +	/*
> +	 * This is analogous to e51527233804 ("drm/xe/guc/ct: Flush g2h worker
> +	 * in case of g2h response timeout")
> +	 *
> +	 * TODO: Drop this change once workqueue scheduling delay issue is
> +	 * fixed on LNL Hybrid CPU.
> +	 */
> +	flush_work(&gt->uc.guc.ct.g2h_worker);

I didn't get the idea of flushing g2h worker here. Moreover AFAIK tlb 
invalidation is handled in fast path xe_guc_ct_fast_path i.e. in IRQ 
handler itself. Is this change solving the issue.

static inline void xe_guc_ct_irq_handler(struct xe_guc_ct *ct)
{
         if (!xe_guc_ct_enabled(ct))
                 return;

         wake_up_all(&ct->wq);
         queue_work(ct->g2h_wq, &ct->g2h_worker);
         xe_guc_ct_fast_path(ct);
}

Regards,
Badal

> +
>   	spin_lock_irq(&gt->tlb_invalidation.pending_lock);
>   	list_for_each_entry_safe(fence, next,
>   				 &gt->tlb_invalidation.pending_fences, link) {