linux-kernel - Re: [PATCH v2] drm/xe: Replace use of system_wq with tlb_inval->fence_signal

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Message-ID: <aWFO5bWNIy+N5/AS@lstrano-desk.jf.intel.com>
Date: Fri, 9 Jan 2026 10:54:29 -0800
From: Matthew Brost <matthew.brost@...el.com>
To: Marco Crivellari <marco.crivellari@...e.com>
CC: <linux-kernel@...r.kernel.org>, <intel-xe@...ts.freedesktop.org>,
	<dri-devel@...ts.freedesktop.org>, Tejun Heo <tj@...nel.org>, Lai Jiangshan
	<jiangshanlai@...il.com>, Frederic Weisbecker <frederic@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Michal Hocko
	<mhocko@...e.com>, Thomas Hellstrom <thomas.hellstrom@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Subject: Re: [PATCH v2] drm/xe: Replace use of system_wq with
 tlb_inval->fence_signal_wq

On Fri, Jan 09, 2026 at 04:57:17PM +0100, Marco Crivellari wrote:
> This patch continues the effort to refactor workqueue APIs, which has begun
> with the changes introducing new workqueues and a new alloc_workqueue flag:
> 
>    commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
>    commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
> 
> The point of the refactoring is to eventually alter the default behavior of
> workqueues to become unbound by default so that their workload placement is
> optimized by the scheduler.
> 
> Before that to happen, workqueue users must be converted to the better named
> new workqueues with no intended behaviour changes:
> 
>    system_wq -> system_percpu_wq
>    system_unbound_wq -> system_dfl_wq
> 
> This way the old obsolete workqueues (system_wq, system_unbound_wq) can be
> removed in the future.
> 
> After a carefully evaluation, because this is the fence signaling path, we
> changed the code in order to use one of the Xe's workqueue.
> 
> So, a new workqueue named 'fence_signal_wq' has been added to
> 'struct xe_tlb_inval' and has been initialized with 'gt->ordered_wq'
> changing the system_wq uses with tlb_inval->fence_signal_wq.
> 
> Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
> Changes in v2:
> - added 'fence_signal_wq', initialized with 'gt->ordered_wq' in order to use
>   it in the fence signaling path, instead of system_wq.
> 
> - rebased on v6.19-rc4
> 
> 
>  drivers/gpu/drm/xe/xe_tlb_inval.c       | 10 +++++++---
>  drivers/gpu/drm/xe/xe_tlb_inval_types.h |  2 ++
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_tlb_inval.c b/drivers/gpu/drm/xe/xe_tlb_inval.c
> index 918a59e686ea..2e98f407c59d 100644
> --- a/drivers/gpu/drm/xe/xe_tlb_inval.c
> +++ b/drivers/gpu/drm/xe/xe_tlb_inval.c
> @@ -94,7 +94,7 @@ static void xe_tlb_inval_fence_timeout(struct work_struct *work)
>  		xe_tlb_inval_fence_signal(fence);
>  	}
>  	if (!list_empty(&tlb_inval->pending_fences))
> -		queue_delayed_work(system_wq, &tlb_inval->fence_tdr,
> +		queue_delayed_work(tlb_inval->fence_signal_wq, &tlb_inval->fence_tdr,
>  				   timeout_delay);
>  	spin_unlock_irq(&tlb_inval->pending_lock);
>  }
> @@ -146,6 +146,10 @@ int xe_gt_tlb_inval_init_early(struct xe_gt *gt)
>  	if (IS_ERR(tlb_inval->job_wq))
>  		return PTR_ERR(tlb_inval->job_wq);
>  
> +	tlb_inval->fence_signal_wq = gt->ordered_wq;
> +	if (IS_ERR(tlb_inval->fence_signal_wq))
> +		return PTR_ERR(tlb_inval->fence_signal_wq);
> +
>  	/* XXX: Blindly setting up backend to GuC */
>  	xe_guc_tlb_inval_init_early(&gt->uc.guc, tlb_inval);
>  
> @@ -226,7 +230,7 @@ static void xe_tlb_inval_fence_prep(struct xe_tlb_inval_fence *fence)
>  	list_add_tail(&fence->link, &tlb_inval->pending_fences);
>  
>  	if (list_is_singular(&tlb_inval->pending_fences))
> -		queue_delayed_work(system_wq, &tlb_inval->fence_tdr,
> +		queue_delayed_work(tlb_inval->fence_signal_wq, &tlb_inval->fence_tdr,
>  				   tlb_inval->ops->timeout_delay(tlb_inval));
>  	spin_unlock_irq(&tlb_inval->pending_lock);
>  
> @@ -378,7 +382,7 @@ void xe_tlb_inval_done_handler(struct xe_tlb_inval *tlb_inval, int seqno)
>  	}
>  
>  	if (!list_empty(&tlb_inval->pending_fences))
> -		mod_delayed_work(system_wq,
> +		mod_delayed_work(tlb_inval->fence_signal_wq,
>  				 &tlb_inval->fence_tdr,
>  				 tlb_inval->ops->timeout_delay(tlb_inval));
>  	else
> diff --git a/drivers/gpu/drm/xe/xe_tlb_inval_types.h b/drivers/gpu/drm/xe/xe_tlb_inval_types.h
> index 8f8b060e9005..1a3e239ea3a7 100644
> --- a/drivers/gpu/drm/xe/xe_tlb_inval_types.h
> +++ b/drivers/gpu/drm/xe/xe_tlb_inval_types.h
> @@ -106,6 +106,8 @@ struct xe_tlb_inval {
>  	struct workqueue_struct *job_wq;
>  	/** @tlb_inval.lock: protects TLB invalidation fences */
>  	spinlock_t lock;
> +	/** @fence_signal_wq: schedule fence signaling path jobs  */
> +	struct workqueue_struct *fence_signal_wq;

I hate to be nitpicky but this name / kernel doc isn't great.

How about:

/** @timeout_wq: schedules TLB invalidation fence timeouts */
struct workqueue_struct *timeout_wq;

Functionality everything in this patch looks correct.

Matt

>  };
>  
>  /**
> -- 
> 2.52.0
>