Re: [PATCH] drm/xe: Skip GT TLB invalidation when VM has no queues mapped

["Summers, Stuart" <stuart.summers@intel.com>]

On Wed, 2026-08-05 at 20:32 -0700, Matthew Brost wrote:
> If no exec queues from a VM are mapped on a GT, issuing a PPGTT TLB
> invalidation for that GT can require an rc6 wake which is expensive.
> 
> Skip the media TLB invalidation when the VM has no exec queues
> mapped on it. If TLB invalidations are already in-flight on that GT
> we can't break fence ordering, so issue a dummy GGTT invalidation
> instead to maintain seqno ordering.
> 
> This optimization is particularly impactful for SVM workloads which
> may or may not use the media GT. Average TLB invalidation time drops
> from ~75us to ~18us in such benchmarks on certain BMG parts - the
> improvement varies based on platform.

Still going through the code changes, but is there a chance we could
deregister a context (so no queues exist), then mmap to invalidate,
then register a new context and read stale data here? I think in the
context invalidation case where we don't have queues we would normally
send a full invalidation instead rather than just skipping it. That
seems risky...

Thanks,
Stuart

> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> 
> ---
> v2:
>  - Make GT generic rather than just media GT (Thomas)
>  - Fix accounting bug in empty vs non-empty (CI)
> ---
>  drivers/gpu/drm/xe/xe_guc_tlb_inval.c | 20 ++++++++++++++++++--
>  drivers/gpu/drm/xe/xe_vm.c            | 12 ++----------
>  2 files changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> b/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> index 046d0655122f..ab04b87cf1c3 100644
> --- a/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> +++ b/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> @@ -205,11 +205,27 @@ static int send_tlb_inval_asid_ppgtt(struct
> xe_tlb_inval *tlb_inval, u32 seqno,
>                                      struct drm_suballoc *prl_sa)
>  {
>         struct xe_guc *guc = tlb_inval->private;
> +       struct xe_device *xe = guc_to_xe(guc);
> +       struct xe_vm *vm;
> +       int err, id = guc_to_gt(guc)->info.id;
>  
>         lockdep_assert_held(&tlb_inval->seqno_lock);
>  
> -       return send_tlb_inval_ppgtt(guc, seqno, start, end, asid,
> -                                   XE_GUC_TLB_INVAL_PAGE_SELECTIVE,
> prl_sa);
> +       vm = xe_device_asid_to_vm(xe, asid);
> +       if (IS_ERR(vm))
> +               return PTR_ERR(vm);
> +
> +       down_read(&vm->exec_queues.lock);
> +       if (!vm->exec_queues.count[id] &&
> xe_tlb_inval_idle(tlb_inval))
> +               err = -ECANCELED;
> +       else
> +               err = send_tlb_inval_ppgtt(guc, seqno, start, end,
> asid,
> +                                         
> XE_GUC_TLB_INVAL_PAGE_SELECTIVE,
> +                                          prl_sa);
> +       up_read(&vm->exec_queues.lock);
> +       xe_vm_put(vm);
> +
> +       return err;
>  }
>  
>  static int send_tlb_inval_ctx_ppgtt(struct xe_tlb_inval *tlb_inval,
> u32 seqno,
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 9e0176861cb6..e2667200462c 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -4946,8 +4946,7 @@ int xe_vm_alloc_cpu_addr_mirror_vma(struct
> xe_vm *vm, uint64_t start, uint64_t r
>   * @vm: The VM.
>   * @q: The exec_queue
>   *
> - * Add exec queue to VM, skipped if the device does not have context
> based TLB
> - * invalidations.
> + * Add exec queue to VM.
>   */
>  void xe_vm_add_exec_queue(struct xe_vm *vm, struct xe_exec_queue *q)
>  {
> @@ -4961,9 +4960,6 @@ void xe_vm_add_exec_queue(struct xe_vm *vm,
> struct xe_exec_queue *q)
>         xe_assert(xe, vm->xef);
>         xe_assert(xe, vm == q->vm);
>  
> -       if (!xe->info.has_ctx_tlb_inval)
> -               return;
> -
>         down_write(&vm->exec_queues.lock);
>         list_add(&q->vm_exec_queue_link, &vm->exec_queues.list[q->gt-
> >info.id]);
>         ++vm->exec_queues.count[q->gt->info.id];
> @@ -4975,14 +4971,10 @@ void xe_vm_add_exec_queue(struct xe_vm *vm,
> struct xe_exec_queue *q)
>   * @vm: The VM.
>   * @q: The exec_queue
>   *
> - * Remove exec queue from VM, skipped if the device does not have
> context based
> - * TLB invalidations.
> + * Remove exec queue from VM.
>   */
>  void xe_vm_remove_exec_queue(struct xe_vm *vm, struct xe_exec_queue
> *q)
>  {
> -       if (!vm->xe->info.has_ctx_tlb_inval)
> -               return;
> -
>         down_write(&vm->exec_queues.lock);
>         if (!list_empty(&q->vm_exec_queue_link)) {
>                 list_del(&q->vm_exec_queue_link);