Re: [PATCH v8 4/6] drm/i915: Interrupt driven fences

From: Chris Wilson <chris@chris-wilson.co.uk>
To: John.C.Harrison@Intel.com
Cc: Intel-GFX@Lists.FreeDesktop.Org
Subject: Re: [PATCH v8 4/6] drm/i915: Interrupt driven fences
Date: Fri, 13 May 2016 08:27:20 +0100	[thread overview]
Message-ID: <20160513072720.GG23271@nuc-i3427.alporthouse.com> (raw)
In-Reply-To: <1463087196-11688-5-git-send-email-John.C.Harrison@Intel.com>

On Thu, May 12, 2016 at 10:06:34PM +0100, John.C.Harrison@Intel.com wrote:
> +void i915_gem_request_notify(struct intel_engine_cs *engine, bool fence_locked)
> +{
> +	struct drm_i915_gem_request *req, *req_next;
> +	unsigned long flags;
>  	u32 seqno;
>  
> -	seqno = req->engine->get_seqno(req->engine);
> +	if (list_empty(&engine->fence_signal_list))
> +		return;
> +
> +	if (!fence_locked)
> +		spin_lock_irqsave(&engine->fence_lock, flags);
> +
> +	if (engine->irq_seqno_barrier)
> +		engine->irq_seqno_barrier(engine);
> +	seqno = engine->get_seqno(engine);
> +
> +	list_for_each_entry_safe(req, req_next, &engine->fence_signal_list, signal_link) {

NO, NO, NO. As we said the very first time, you cannot do this from an
irq handler.

The current code is already bad enough, this is making it large constant
+ N times worse. Please do look at how to do signal driven fences in O(1)
that I posted many months ago and several times since.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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