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 10:16:39 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Will Deacon <will@...nel.org>
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 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.

> 
> Will
> .
>