linux-kernel - Re: [PATCH v6 09/10] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active

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Message-ID: <20230821104247.GA19469@willie-the-truck>
Date:   Mon, 21 Aug 2023 11:42:47 +0100
From:   Will Deacon <will@...nel.org>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, robin.murphy@....com,
        jean-philippe@...aro.org, jgg@...dia.com, nicolinc@...dia.com
Subject: Re: [PATCH v6 09/10] iommu/arm-smmu-v3: Skip cd sync if CD table
 isn't active

On Mon, Aug 21, 2023 at 06:16:08PM +0800, Michael Shavit wrote:
> On Wed, Aug 16, 2023 at 9:20 PM Michael Shavit <mshavit@...gle.com> wrote:
> >
> > This commit explicitly keeps track of whether a CD table is installed in
> > an STE so that arm_smmu_sync_cd can skip the sync when unnecessary. This
> > was previously achieved through the domain->devices list, but we are
> > moving to a model where arm_smmu_sync_cd directly operates on a master
> > and the master's CD table instead of a domain.
> >
> > Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> > Reviewed-by: Nicolin Chen <nicolinc@...dia.com>
> > Signed-off-by: Michael Shavit <mshavit@...gle.com>
> > ---
> > Happy to drop this commit if we don't think it's useful.
> 
> Hi Will,
> Do you have any recommendations for keeping or dropping this commit in
> the end? It's only purpose is to minimize any potential performance
> impact from the refactor but can certainly be dropped if you don't
> think it's worth the complication.

I'd prefer to drop it unless somebody can measure the benefits that it
brings.

Will