linux-kernel - Re: [PATCH RFC 2/8] iommu/arm-smmu-v3: Add and use static helper function arm_smmu_cmdq_issue_cmd_with

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Date:   Wed, 11 Aug 2021 11:09:06 +0100
From:   Will Deacon <will@...nel.org>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 2/8] iommu/arm-smmu-v3: Add and use static helper
 function arm_smmu_cmdq_issue_cmd_with_sync()

On Wed, Aug 11, 2021 at 10:16:39AM +0800, Leizhen (ThunderTown) wrote:
> 
> 
> On 2021/8/11 2:24, Will Deacon wrote:
> > On Sat, Jun 26, 2021 at 07:01:24PM +0800, Zhen Lei wrote:
> >> The obvious key to the performance optimization of commit 587e6c10a7ce
> >> ("iommu/arm-smmu-v3: Reduce contention during command-queue insertion") is
> >> to allow multiple cores to insert commands in parallel after a brief mutex
> >> contention.
> >>
> >> Obviously, inserting as many commands at a time as possible can reduce the
> >> number of times the mutex contention participates, thereby improving the
> >> overall performance. At least it reduces the number of calls to function
> >> arm_smmu_cmdq_issue_cmdlist().
> >>
> >> Therefore, function arm_smmu_cmdq_issue_cmd_with_sync() is added to insert
> >> the 'cmd+sync' commands at a time.
> >>
> >> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> >> ---
> >>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 33 +++++++++++++--------
> >>  1 file changed, 21 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >> index 2433d3c29b49ff2..a5361153ca1d6a4 100644
> >> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> >> @@ -858,11 +858,25 @@ static int arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
> >>  	return arm_smmu_cmdq_issue_cmdlist(smmu, cmd, 1, false);
> >>  }
> >>  
> >> -static int arm_smmu_cmdq_issue_sync(struct arm_smmu_device *smmu)
> >> +static int __maybe_unused arm_smmu_cmdq_issue_sync(struct arm_smmu_device *smmu)
> >>  {
> >>  	return arm_smmu_cmdq_issue_cmdlist(smmu, NULL, 0, true);
> >>  }
> >>  
> >> +static int arm_smmu_cmdq_issue_cmd_with_sync(struct arm_smmu_device *smmu,
> >> +					     struct arm_smmu_cmdq_ent *ent)
> >> +{
> >> +	u64 cmd[CMDQ_ENT_DWORDS];
> >> +
> >> +	if (arm_smmu_cmdq_build_cmd(cmd, ent)) {
> >> +		dev_warn(smmu->dev, "ignoring unknown CMDQ opcode 0x%x\n",
> >> +			 ent->opcode);
> >> +		return -EINVAL;
> >> +	}
> >> +
> >> +	return arm_smmu_cmdq_issue_cmdlist(smmu, cmd, 1, true);
> >> +}
> > 
> > This function is almost identical to arm_smmu_cmdq_issue_cmd(). How about
> > moving the guts out into a helper:
> > 
> > 	static int __arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
> > 					     struct arm_smmu_cmdq_ent *ent,
> > 					     bool sync);
> > 
> > and then having arm_smmu_cmdq_issue_cmd_with_sync() and
> > arm_smmu_cmdq_issue_cmd() wrap that?
> 
> OK, I will do it.
> 
> How about remove arm_smmu_cmdq_issue_sync()? It's unused now.

Sure.

Will