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

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Date:   Mon, 28 Oct 2019 15:38:04 -0700
From:   Rob Clark <robdclark@...omium.org>
To:     Will Deacon <will@...nel.org>
Cc:     Rob Clark <robdclark@...il.com>, iommu@...ts.linux-foundation.org,
        freedreno <freedreno@...ts.freedesktop.org>,
        Robin Murphy <robin.murphy@....com>,
        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 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"?

BR,
-R


>
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> > v1: original
> > v2: unconditionally use autosuspend, rather than deciding based on what
> >     consumer does
> >
> >  drivers/iommu/arm-smmu.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > index 3f1d55fb43c4..b7b41f5001bc 100644
> > --- a/drivers/iommu/arm-smmu.c
> > +++ b/drivers/iommu/arm-smmu.c
> > @@ -289,7 +289,7 @@ static inline int arm_smmu_rpm_get(struct arm_smmu_device *smmu)
> >  static inline void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
> >  {
> >       if (pm_runtime_enabled(smmu->dev))
> > -             pm_runtime_put(smmu->dev);
> > +             pm_runtime_put_autosuspend(smmu->dev);
> >  }
> >
> >  static struct arm_smmu_domain *to_smmu_domain(struct iommu_domain *dom)
> > @@ -1445,6 +1445,9 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >       /* Looks ok, so add the device to the domain */
> >       ret = arm_smmu_domain_add_master(smmu_domain, fwspec);
>
> Please can you put a comment here explaining what this is doing? An abridged
> version of the commit message is fine.
>
> > +     pm_runtime_set_autosuspend_delay(smmu->dev, 20);
> > +     pm_runtime_use_autosuspend(smmu->dev);
>
> Cheers,
>
> Will