From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Subject: Re: [benjamin.widawsky@intel.com: intel_gpu_top broken
	for HSW. Ideas needed]
Date: Mon, 15 Jul 2013 12:42:16 +0300
Message-ID: <87ip0cgnwn.fsf@gaia.fi.intel.com>
References: <20130712171239.GA15328@intel.com>
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To: Ben Widawsky <benjamin.widawsky@intel.com>, Intel GFX <intel-gfx@lists.freedesktop.org>
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Ben Widawsky <benjamin.widawsky@intel.com> writes:

> FWD'd from our internal list now that we have more insight.
> ----- Forwarded message from Ben Widawsky <benjamin.widawsky@intel.com> -----
>
> Date: Thu, 11 Jul 2013 10:32:03 -0700
> From: Ben Widawsky <benjamin.widawsky@intel.com>
> To: linux-gfx@linux.intel.com
> Subject: intel_gpu_top broken for HSW. Ideas needed
> Message-ID: <20130711173202.GB8802@intel.com>
>
> Hi everybody.
>
> While investigating a hard hang on Haswell. Eero noticed that
> intel_gpu_top helped to invoke the hang faster. I used this in my test
> case to validation, and they are suspecting it is a known issue which we
> have not yet worked around (and cannot reasonably workaround).
>
> [internal bug sighting redacted]
>
> To sum up, we cannot concurrently access registers within the same
> cacheline. It has the potential to hit a known bug.
>
> I see some choices:
> 1. Don't do anything.
> 2. Try to eliminate shared registers as much as possible. Instdone is
>    used by the hangcheck, and we can eliminate hangcheck with a
>    module parameter. Eero, can you try this as a workaround, btw?

Commit: 92cab7345131db7af18f630a799ce6b2e8e624c5 gets rid of
instdone on hangcheck.

-Mika

> 3. Somehow make the kernel collect the top data and serialize access
>    there.
>
> Anyone else have input? I personally do not use top very much, so I
> won't be volunteering to do any of these.
>
> ----- End forwarded message -----
>
> -- 
> Ben Widawsky, Intel Open Source Technology Center
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