Messages in this thread | | | Subject | Re: [PATCH 1/4] iommu/arm-smmu-v3: Use command queue batching helpers to improve performance | From | John Garry <> | Date | Mon, 16 Aug 2021 08:24:28 +0100 |
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> 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.
> > 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 >
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