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From: John Garry <john.garry@huawei.com>
To: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Will Deacon <will@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	iommu <iommu@lists.linux-foundation.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/4] iommu/arm-smmu-v3: Use command queue batching helpers to improve performance
Date: Mon, 16 Aug 2021 08:24:28 +0100	[thread overview]
Message-ID: <a3cdd5df-c028-5484-ce99-928a689d341a@huawei.com> (raw)
In-Reply-To: <52204403-f69a-d2b9-9365-7553e87d1298@huawei.com>

> In addition, I find that function arm_smmu_cmdq_build_cmd() can also be optimized
> slightly, three useless instructions can be reduced.

I think that you could optimise further by pre-building commonly used 
commands.

For example, CMD_SYNC without MSI polling is always the same. And then 
only different in 1 field for MSI polling.

But you need to check if the performance gain is worth the change.

> 
> Case 1):
> void arm_smmu_cmdq_build_cmd_tst1(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
> {
>          memset(cmd, 0, 1 << CMDQ_ENT_SZ_SHIFT);
>          cmd[0] |= FIELD_PREP(CMDQ_0_OP, ent->opcode);
> }
> 0000000000004608 <arm_smmu_cmdq_build_cmd_tst1>:
>      4608:       a9007c1f        stp     xzr, xzr, [x0]
>      460c:       39400022        ldrb    w2, [x1]
>      4610:       f9400001        ldr     x1, [x0]
>      4614:       aa020021        orr     x1, x1, x2
>      4618:       f9000001        str     x1, [x0]
>      461c:       d65f03c0        ret
> 
> Case 2):
> void arm_smmu_cmdq_build_cmd_tst2(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
> {
>          int i;
> 
>          cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
>          for (i = 1; i < CMDQ_ENT_DWORDS; i++)
>                  cmd[i] = 0;
> }
> 0000000000004620 <arm_smmu_cmdq_build_cmd_tst2>:
>      4620:       39400021        ldrb    w1, [x1]
>      4624:       a9007c01        stp     x1, xzr, [x0]
>      4628:       d65f03c0        ret
>      462c:       d503201f        nop
> 
> Case 3):
> void arm_smmu_cmdq_build_cmd_tst3(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
> {
>          memset(cmd, 0, 1 << CMDQ_ENT_SZ_SHIFT);
>          cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
> }
> 0000000000004630 <arm_smmu_cmdq_build_cmd_tst3>:
>      4630:       a9007c1f        stp     xzr, xzr, [x0]
>      4634:       39400021        ldrb    w1, [x1]
>      4638:       f9000001        str     x1, [x0]
>      463c:       d65f03c0        ret
> 


  reply	other threads:[~2021-08-16  7:25 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-11 11:48 [PATCH 0/4] Prepare for ECMDQ support Zhen Lei
2021-08-11 11:48 ` [PATCH 1/4] iommu/arm-smmu-v3: Use command queue batching helpers to improve performance Zhen Lei
2021-08-13 16:01   ` Robin Murphy
2021-08-13 16:45     ` John Garry
2021-08-16  2:15       ` Leizhen (ThunderTown)
2021-08-16  4:05         ` Leizhen (ThunderTown)
2021-08-16  7:24           ` John Garry [this message]
2021-08-16  7:47             ` Leizhen (ThunderTown)
2021-08-16  8:21               ` Will Deacon
2021-08-16  8:41                 ` Leizhen (ThunderTown)
2021-08-11 11:48 ` [PATCH 2/4] iommu/arm-smmu-v3: Add and use static helper function arm_smmu_cmdq_issue_cmd_with_sync() Zhen Lei
2021-08-11 11:48 ` [PATCH 3/4] iommu/arm-smmu-v3: Add and use static helper function arm_smmu_get_cmdq() Zhen Lei
2021-08-11 11:48 ` [PATCH 4/4] iommu/arm-smmu-v3: Extract reusable function __arm_smmu_cmdq_skip_err() Zhen Lei
2021-08-13 14:33 ` [PATCH 0/4] Prepare for ECMDQ support Will Deacon

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