linux-kernel - Re: [PATCH 1/4] iommu/arm-smmu-v3: Use command queue batching helpers to improve performance

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Message-ID: <52204403-f69a-d2b9-9365-7553e87d1298@huawei.com>
Date:   Mon, 16 Aug 2021 12:05:33 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     John Garry <john.garry@...wei.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] iommu/arm-smmu-v3: Use command queue batching helpers
 to improve performance

On 2021/8/16 10:15, Leizhen (ThunderTown) wrote:
> 
> 
> On 2021/8/14 0:45, John Garry wrote:
>> On 13/08/2021 17:01, Robin Murphy wrote:
>>>>
>>>> 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 235f9bdaeaf223b..c81cd929047f573 100644
>>>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>>> @@ -1747,15 +1747,16 @@ static int arm_smmu_atc_inv_master(struct arm_smmu_master *master)
>>>>   {
>>>>       int i;
>>>>       struct arm_smmu_cmdq_ent cmd;
>>>> +    struct arm_smmu_cmdq_batch cmds = {};
>>>
>>> BTW, it looks like this has crossed over with John's patch removing these.
>>
>> It is only called from arm_smmu_disable_ats(), so not hot-path by the look for it. Or who even has ats HW ...?
>>
>> But it should be at least cleaned-up for consistency. Leizhen?
> 
> Okay, I'll revise it. But Will already took it. So I'm not sure whether to send v2 or a separate patch.

I think I'd better post v2, otherwise I should write the same description.

In addition, I find that function arm_smmu_cmdq_build_cmd() can also be optimized
slightly, three useless instructions can be reduced.

Case 1):
void arm_smmu_cmdq_build_cmd_tst1(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
{
        memset(cmd, 0, 1 << CMDQ_ENT_SZ_SHIFT);
        cmd[0] |= FIELD_PREP(CMDQ_0_OP, ent->opcode);
}
0000000000004608 <arm_smmu_cmdq_build_cmd_tst1>:
    4608:       a9007c1f        stp     xzr, xzr, [x0]
    460c:       39400022        ldrb    w2, [x1]
    4610:       f9400001        ldr     x1, [x0]
    4614:       aa020021        orr     x1, x1, x2
    4618:       f9000001        str     x1, [x0]
    461c:       d65f03c0        ret

Case 2):
void arm_smmu_cmdq_build_cmd_tst2(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
{
        int i;

        cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
        for (i = 1; i < CMDQ_ENT_DWORDS; i++)
                cmd[i] = 0;
}
0000000000004620 <arm_smmu_cmdq_build_cmd_tst2>:
    4620:       39400021        ldrb    w1, [x1]
    4624:       a9007c01        stp     x1, xzr, [x0]
    4628:       d65f03c0        ret
    462c:       d503201f        nop

Case 3):
void arm_smmu_cmdq_build_cmd_tst3(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
{
        memset(cmd, 0, 1 << CMDQ_ENT_SZ_SHIFT);
        cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
}
0000000000004630 <arm_smmu_cmdq_build_cmd_tst3>:
    4630:       a9007c1f        stp     xzr, xzr, [x0]
    4634:       39400021        ldrb    w1, [x1]
    4638:       f9000001        str     x1, [x0]
    463c:       d65f03c0        ret

> 
>>
>> Thanks,
>> John
>> .
>>
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
> 

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