Messages in this thread | | | Subject | Re: [PATCH v4 2/2] iommu/arm-smmu-v3: avoid redundant CMD_SYNCs if possible | From | "Leizhen (ThunderTown)" <> | Date | Wed, 5 Sep 2018 09:15:20 +0800 |
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On 2018/8/30 19:18, John Garry wrote: > On 19/08/2018 08:51, Zhen Lei wrote: >> spin_unlock_irqrestore(&smmu->cmdq.lock, flags); > > I find something like this adds support for combining CMD_SYNC commands for regular polling mode: > > @@ -569,6 +569,7 @@ struct arm_smmu_device { > int combined_irq; > u32 sync_nr; > u8 prev_cmd_opcode; > + int prev_cmd_sync_res; > > unsigned long ias; /* IPA */ > unsigned long oas; /* PA */ > @@ -985,17 +986,33 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu) > > static int __arm_smmu_cmdq_issue_sync(struct arm_smmu_device *smmu) > { > - u64 cmd[CMDQ_ENT_DWORDS]; > + static u64 cmd[CMDQ_ENT_DWORDS] = { > + _FIELD_PREP(CMDQ_0_OP, CMDQ_OP_CMD_SYNC) | > + _FIELD_PREP(CMDQ_SYNC_0_CS, CMDQ_SYNC_0_CS_SEV) | > + _FIELD_PREP(CMDQ_SYNC_0_MSH, ARM_SMMU_SH_ISH) | > + _FIELD_PREP(CMDQ_SYNC_0_MSIATTR, ARM_SMMU_MEMATTR_OIWB) > + }; > unsigned long flags; > bool wfe = !!(smmu->features & ARM_SMMU_FEAT_SEV); > - struct arm_smmu_cmdq_ent ent = { .opcode = CMDQ_OP_CMD_SYNC }; > - int ret; > + int ret = 0; > > - arm_smmu_cmdq_build_cmd(cmd, &ent); > > spin_lock_irqsave(&smmu->cmdq.lock, flags); > - arm_smmu_cmdq_insert_cmd(smmu, cmd); > - ret = queue_poll_cons(&smmu->cmdq.q, true, wfe); > + if (smmu->prev_cmd_opcode != CMDQ_OP_CMD_SYNC || > + smmu->prev_cmd_sync_res != 0) { > + arm_smmu_cmdq_insert_cmd(smmu, cmd); > + smmu->prev_cmd_sync_res = ret = > + queue_poll_cons(&smmu->cmdq.q, true, wfe); > + } > > I tested iperf on a 1G network link and was seeing 6-10% CMD_SYNC commands combined. I would really need to test this on a faster connection to see any throughout difference. > > From the above figures, I think leizhen was seeing 25% combine rate, right?
Yes. In my test case, the size of unmap are almost one page, that means 1 TLBI follows 1 SYNC, so the probability that two CMD_SYNCs next to each other will be greater.
> > As for this code, it could be neatened... > > Cheers, > John > >> >> return __arm_smmu_sync_poll_msi(smmu, ent.sync.msidata); >> -- >> 1.8.3 >> >> >> >> . >> > > > > . >
-- Thanks! BestRegards
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