From: John Garry <john.garry@huawei.com>
To: Will Deacon <will@kernel.org>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>,
Marc Zyngier <maz@kernel.org>, Ming Lei <ming.lei@redhat.com>,
iommu@lists.linux-foundation.org,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: arm-smmu-v3 high cpu usage for NVMe
Date: Thu, 19 Mar 2020 12:54:59 +0000
Message-ID: <c6ab8020-dc06-0c7d-7a41-e792d90f97ba@huawei.com> (raw)
In-Reply-To: <20200318205313.GB8094@willie-the-truck>
Hi Will,
>
> On Thu, Jan 02, 2020 at 05:44:39PM +0000, John Garry wrote:
>> And for the overall system, we have:
>>
>> PerfTop: 85864 irqs/sec kernel:89.6% exact: 0.0% lost: 0/34434 drop:
>> 0/40116 [4000Hz cycles], (all, 96 CPUs)
>> --------------------------------------------------------------------------------------------------------------------------
>>
>> 27.43% [kernel] [k] arm_smmu_cmdq_issue_cmdlist
>> 11.71% [kernel] [k] _raw_spin_unlock_irqrestore
>> 6.35% [kernel] [k] _raw_spin_unlock_irq
>> 2.65% [kernel] [k] get_user_pages_fast
>> 2.03% [kernel] [k] __slab_free
>> 1.55% [kernel] [k] tick_nohz_idle_exit
>> 1.47% [kernel] [k] arm_lpae_map
>> 1.39% [kernel] [k] __fget
>> 1.14% [kernel] [k] __lock_text_start
>> 1.09% [kernel] [k] _raw_spin_lock
>> 1.08% [kernel] [k] bio_release_pages.part.42
>> 1.03% [kernel] [k] __sbitmap_get_word
>> 0.97% [kernel] [k] arm_smmu_atc_inv_domain.constprop.42
>> 0.91% [kernel] [k] fput_many
>> 0.88% [kernel] [k] __arm_lpae_map
>>
>> One thing to note is that we still spend an appreciable amount of time in
>> arm_smmu_atc_inv_domain(), which is disappointing when considering it should
>> effectively be a noop.
>>
>> As for arm_smmu_cmdq_issue_cmdlist(), I do note that during the testing our
>> batch size is 1, so we're not seeing the real benefit of the batching. I
>> can't help but think that we could improve this code to try to combine CMD
>> SYNCs for small batches.
>>
>> Anyway, let me know your thoughts or any questions. I'll have a look if a
>> get a chance for other possible bottlenecks.
>
> Did you ever get any more information on this? I don't have any SMMUv3
> hardware any more, so I can't really dig into this myself.
I'm only getting back to look at this now, as SMMU performance is a bit
of a hot topic again for us.
So one thing we are doing which looks to help performance is this series
from Marc:
https://lore.kernel.org/lkml/9171c554-50d2-142b-96ae-1357952fce52@huawei.com/T/#mee5562d1efd6aaeb8d2682bdb6807fe7b5d7f56d
So that is just spreading the per-CPU load for NVMe interrupt handling
(where the DMA unmapping is happening), so I'd say just side-stepping
any SMMU issue really.
Going back to the SMMU, I wanted to run epbf and perf annotate to help
profile this, but was having no luck getting them to work properly. I'll
look at this again now.
Cheers,
John
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Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 15:17 [PATCH v2 0/8] Sort out SMMUv3 ATC invalidation and locking Will Deacon
2019-08-21 15:17 ` [PATCH v2 1/8] iommu/arm-smmu-v3: Document ordering guarantees of command insertion Will Deacon
2019-08-21 15:17 ` [PATCH v2 2/8] iommu/arm-smmu-v3: Disable detection of ATS and PRI Will Deacon
2019-08-21 15:36 ` Robin Murphy
2019-08-21 15:17 ` [PATCH v2 3/8] iommu/arm-smmu-v3: Remove boolean bitfield for 'ats_enabled' flag Will Deacon
2019-08-21 15:17 ` [PATCH v2 4/8] iommu/arm-smmu-v3: Don't issue CMD_SYNC for zero-length invalidations Will Deacon
2019-08-21 15:17 ` [PATCH v2 5/8] iommu/arm-smmu-v3: Rework enabling/disabling of ATS for PCI masters Will Deacon
2019-08-21 15:50 ` Robin Murphy
2019-08-21 15:17 ` [PATCH v2 6/8] iommu/arm-smmu-v3: Fix ATC invalidation ordering wrt main TLBs Will Deacon
2019-08-21 16:25 ` Robin Murphy
2019-08-21 15:17 ` [PATCH v2 7/8] iommu/arm-smmu-v3: Avoid locking on invalidation path when not using ATS Will Deacon
2019-08-22 12:36 ` Robin Murphy
2019-08-21 15:17 ` [PATCH v2 8/8] Revert "iommu/arm-smmu-v3: Disable detection of ATS and PRI" Will Deacon
2020-01-02 17:44 ` arm-smmu-v3 high cpu usage for NVMe John Garry
2020-03-18 20:53 ` Will Deacon
2020-03-19 12:54 ` John Garry [this message]
2020-03-19 18:43 ` Jean-Philippe Brucker
2020-03-20 10:41 ` John Garry
2020-03-20 11:18 ` Jean-Philippe Brucker
2020-03-20 16:20 ` John Garry
2020-03-20 16:33 ` Marc Zyngier
2020-03-23 9:03 ` John Garry
2020-03-23 9:16 ` Marc Zyngier
2020-03-24 9:18 ` John Garry
2020-03-24 10:43 ` Marc Zyngier
2020-03-24 11:55 ` John Garry
2020-03-24 12:07 ` Robin Murphy
2020-03-24 12:37 ` John Garry
2020-03-25 15:31 ` John Garry
2020-05-22 14:52 ` John Garry
2020-05-25 5:57 ` Song Bao Hua (Barry Song)
[not found] ` <482c00d5-8e6d-1484-820e-1e89851ad5aa@huawei.com>
2020-04-06 15:11 ` John Garry
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