From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH 0/4] [RFC] use HW watchdog timer
Date: Tue, 17 Jul 2012 12:12:39 +0100
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Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, Ben Widawsky <ben@bwidawsk.net>
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On Mon, 16 Jul 2012 11:51:55 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> Pros:
> * Potential for per batch, or ring watchdog values. I believe when/if we
> get to GPGPU workloads, this is particularly interesting.
> * Batch granularity hang detection. This mostly just makes hang
> detection and recovery a bit easier IMO.
> 
> Cons:
> * Blit ring doesn't have an interrupt. This means we still need the
> software watchdog, and it makes hang detection more complex. I've been
> led to believe future HW *may* have this interrupt.
> * Semaphores 

Replacing the black magic for INSTDONE hang detection does seem like a
sensible plan, but as long as we require the hangcheck timer we are only
adding code complexity. So there really needs to a be a compelling
advantage for the watchdoy, something that we cannot acheive with the
existing method.

For me, the criteria is whether we ever miss a hang or falsely accuse
the hw of stopping. If I understand the watchdog correctly, it basically
ensures the batch completes within a certain interval which we can
codify into the existing hangcheck, so no USP.

Or is there more magic waiting in the wings?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre