linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Remove some unneeded init in arm_smmu_cmdq_issue

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Date:   Thu, 5 Aug 2021 12:21:14 +0100
From:   Will Deacon <will@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     robin.murphy@....com, joro@...tes.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com
Subject: Re: [PATCH] iommu/arm-smmu-v3: Remove some unneeded init in
 arm_smmu_cmdq_issue_cmdlist()

On Thu, Aug 05, 2021 at 11:22:15AM +0100, John Garry wrote:
> On 21/06/2021 17:36, John Garry wrote:
> > Members of struct "llq" will be zero-inited, apart from member max_n_shift.
> > But we write llq.val straight after the init, so it was pointless to zero
> > init those other members. As such, separately init member max_n_shift
> > only.
> > 
> > In addition, struct "head" is initialised to "llq" only so that member
> > max_n_shift is set. But that member is never referenced for "head", so
> > remove any init there.
> > 
> > Removing these initializations is seen as a small performance optimisation,
> > as this code is (very) hot path.
> > 
> 
> Hi Will,
> 
> Any chance you can pick up this small optimisation?

Yup! I've actually queued it locally, but I may end up asking Joerg to take
it directly depending on what else I queue for 5.15. So far, most of the
SMMU stuff is all part of wider refactorings.

Cheers,

Will