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

[Leizhen (ThunderTown)]

On 2021/8/16 15:24, John Garry wrote:
>> In addition, I find that function arm_smmu_cmdq_build_cmd() can also be optimized
>> slightly, three useless instructions can be reduced.
> 
> I think that you could optimise further by pre-building commonly used commands.
> 
> For example, CMD_SYNC without MSI polling is always the same. And then only different in 1 field for MSI polling.
> 
> But you need to check if the performance gain is worth the change.

Good advice. I can give it a try.

> 
>>
>> 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
>>
> 
> .
>