iommu/arm-smmu-v3: Avoid back-to-back CMD_SYNC operations (901510ee) · Commits · 戴 / test

Putting adjacent CMD_SYNCs into the command queue is nonsensical, but can happen when multiple CPUs are inserting commands. Rather than leave the poor old hardware to chew through these operations, we can instead drop the subsequent SYNCs and poll for completion of the first. This has been shown to improve IO performance under pressure, where the number of SYNC operations reduces by about a third: CMD_SYNCs reduced: 19542181 CMD_SYNCs total: 58098548 (include reduced) CMDs total: 116197099 (TLBI:SYNC about 1:1) Signed-off-by:

Zhen Lei <thunder.leizhen@huawei.com> Signed-off-by:

Will Deacon <will.deacon@arm.com>

drivers/iommu/arm-smmu-v3.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -568,6 +568,7 @@ struct arm_smmu_device {
		int gerr_irq;
		int combined_irq;
		u32 sync_nr;
		u8 prev_cmd_opcode;

		unsigned long ias; /* IPA */
		unsigned long oas; /* PA */
		@@ -901,6 +902,8 @@ static void arm_smmu_cmdq_insert_cmd(struct arm_smmu_device smmu, u64 cmd)
		struct arm_smmu_queue *q = &smmu->cmdq.q;
		bool wfe = !!(smmu->features & ARM_SMMU_FEAT_SEV);

		smmu->prev_cmd_opcode = FIELD_GET(CMDQ_0_OP, cmd[0]);

		while (queue_insert_raw(q, cmd) == -ENOSPC) {
		if (queue_poll_cons(q, false, wfe))
		dev_err_ratelimited(smmu->dev, "CMDQ timeout\n");
		@@ -953,9 +956,16 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu)
		};

		spin_lock_irqsave(&smmu->cmdq.lock, flags);

		/* Piggy-back on the previous command if it's a SYNC */
		if (smmu->prev_cmd_opcode == CMDQ_OP_CMD_SYNC) {
		ent.sync.msidata = smmu->sync_nr;
		} else {
		ent.sync.msidata = ++smmu->sync_nr;
		arm_smmu_cmdq_build_cmd(cmd, &ent);
		arm_smmu_cmdq_insert_cmd(smmu, cmd);
		}

		spin_unlock_irqrestore(&smmu->cmdq.lock, flags);

		return __arm_smmu_sync_poll_msi(smmu, ent.sync.msidata);

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