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Date: Thu, 30 Aug 2018 12:18:21 +0100 From: John Garry <john.garry@...wei.com> To: Zhen Lei <thunder.leizhen@...wei.com>, Robin Murphy <robin.murphy@....com>, Will Deacon <will.deacon@....com>, Joerg Roedel <joro@...tes.org>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, iommu <iommu@...ts.linux-foundation.org>, linux-kernel <linux-kernel@...r.kernel.org> CC: LinuxArm <linuxarm@...wei.com>, Hanjun Guo <guohanjun@...wei.com>, Libin <huawei.libin@...wei.com> Subject: Re: [PATCH v4 2/2] iommu/arm-smmu-v3: avoid redundant CMD_SYNCs if possible On 19/08/2018 08:51, Zhen Lei wrote: > More than two CMD_SYNCs maybe adjacent in the command queue, and the first > one has done what others want to do. Drop the redundant CMD_SYNCs can > improve IO performance especially under the pressure scene. > > I did the statistics in my test environment, the number of CMD_SYNCs can > be reduced about 1/3. See below: > 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@...wei.com> > --- > drivers/iommu/arm-smmu-v3.c | 22 +++++++++++++++++++--- > 1 file changed, 19 insertions(+), 3 deletions(-) > > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c > index ac6d6df..f3a56e1 100644 > --- a/drivers/iommu/arm-smmu-v3.c > +++ b/drivers/iommu/arm-smmu-v3.c > @@ -567,6 +567,7 @@ 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 */ > @@ -786,6 +787,11 @@ void arm_smmu_cmdq_build_sync_msi_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent) > cmd[1] = ent->sync.msiaddr & CMDQ_SYNC_1_MSIADDR_MASK; > } > > +static inline u8 arm_smmu_cmd_opcode_get(u64 *cmd) > +{ > + return cmd[0] & CMDQ_0_OP; > +} > + > /* High-level queue accessors */ > static int arm_smmu_cmdq_build_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent) > { > @@ -906,6 +912,8 @@ 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 = arm_smmu_cmd_opcode_get(cmd); > + > while (queue_insert_raw(q, cmd) == -ENOSPC) { > if (queue_poll_cons(q, false, wfe)) > dev_err_ratelimited(smmu->dev, "CMDQ timeout\n"); > @@ -958,9 +966,17 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu) > }; > > spin_lock_irqsave(&smmu->cmdq.lock, flags); > - ent.sync.msidata = ++smmu->sync_nr; > - arm_smmu_cmdq_build_sync_msi_cmd(cmd, &ent); > - arm_smmu_cmdq_insert_cmd(smmu, cmd); > + if (smmu->prev_cmd_opcode == CMDQ_OP_CMD_SYNC) { > + /* > + * Previous command is CMD_SYNC also, there is no need to add > + * one more. Just poll it. > + */ > + ent.sync.msidata = smmu->sync_nr; > + } else { > + ent.sync.msidata = ++smmu->sync_nr; > + arm_smmu_cmdq_build_sync_msi_cmd(cmd, &ent); > + arm_smmu_cmdq_insert_cmd(smmu, cmd); > + } > 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? As for this code, it could be neatened... Cheers, John > > return __arm_smmu_sync_poll_msi(smmu, ent.sync.msidata); > -- > 1.8.3 > > > > . >
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