lkml.org 
[lkml]   [2018]   [Sep]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v4 2/2] iommu/arm-smmu-v3: avoid redundant CMD_SYNCs if possible
From
Date


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

\
 
 \ /
  Last update: 2018-09-05 03:16    [W:0.075 / U:1.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site