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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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