linux-kernel - Re: [PATCH v2] iommu/arm-smmu: fix "hang" when games exit

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Date:   Mon, 28 Oct 2019 22:51:53 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Rob Clark <robdclark@...omium.org>, Will Deacon <will@...nel.org>
Cc:     Rob Clark <robdclark@...il.com>, iommu@...ts.linux-foundation.org,
        freedreno <freedreno@...ts.freedesktop.org>,
        Joerg Roedel <joro@...tes.org>,
        "moderated list:ARM SMMU DRIVERS" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iommu/arm-smmu: fix "hang" when games exit

On 2019-10-28 10:38 pm, Rob Clark wrote:
> On Mon, Oct 28, 2019 at 3:20 PM Will Deacon <will@...nel.org> wrote:
>>
>> Hi Rob,
>>
>> On Mon, Oct 07, 2019 at 01:49:06PM -0700, Rob Clark wrote:
>>> From: Rob Clark <robdclark@...omium.org>
>>>
>>> When games, browser, or anything using a lot of GPU buffers exits, there
>>> can be many hundreds or thousands of buffers to unmap and free.  If the
>>> GPU is otherwise suspended, this can cause arm-smmu to resume/suspend
>>> for each buffer, resulting 5-10 seconds worth of reprogramming the
>>> context bank (arm_smmu_write_context_bank()/arm_smmu_write_s2cr()/etc).
>>> To the user it would appear that the system just locked up.
>>>
>>> A simple solution is to use pm_runtime_put_autosuspend() instead, so we
>>> don't immediately suspend the SMMU device.
>>
>> Please can you reword the subject to be a bit more useful? The commit
>> message is great, but the subject is a bit like "fix bug in code" to me.
> 
> yeah, not the best $subject, but I wasn't quite sure how to fit
> something better in a reasonable # of chars.. maybe something like:
> "iommu/arm-smmu: optimize unmap but avoiding toggling runpm state"?

FWIW, I'd be inclined to frame it as something like "avoid pathological 
RPM behaviour for unmaps".

Robin.