From: Will Deacon <will@kernel.org>
To: John Garry <john.garry@huawei.com>
Cc: Vijay Kilary <vkilari@codeaurora.org>,
Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
Jon Masters <jcm@redhat.com>, Jan Glauber <jglauber@marvell.com>,
Alex Williamson <alex.williamson@redhat.com>,
iommu@lists.linux-foundation.org,
Jayachandran Chandrasekharan Nair <jnair@marvell.com>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [RFC PATCH v2 18/19] iommu/arm-smmu-v3: Reduce contention during command-queue insertion
Date: Wed, 24 Jul 2019 15:07:52 +0100 [thread overview]
Message-ID: <20190724140751.pewgh4v5bmlmub23@willie-the-truck> (raw)
In-Reply-To: <fa90f89b-77f4-f983-52be-69bb40d17901@huawei.com>
On Wed, Jul 24, 2019 at 03:03:20PM +0100, John Garry wrote:
> On 24/07/2019 13:15, Will Deacon wrote:
> > > Could it be a minor optimisation to advance the HW producer pointer at this
> > > stage for the owner only? We know that its entries are written, and it
> > > should be first in the new batch of commands (right?), so we could advance
> > > the pointer to at least get the HW started.
> >
> > I think that would be a valid thing to do, but it depends on the relative
> > cost of writing to prod compared to how long we're likely to wait. Given
> > that everybody has irqs disabled when writing out their commands, I wouldn't
> > expect the waiting to be a big issue,
>
> For sure, but I'm thinking of the possible scenario where the the guy(s)
> we're waiting on have many more commands. Or they just joined the current
> gathering quite late, just prior to clearing the owner flag.
Understood, but a "cacheable" memcpy (assuming the SMMU is coherent) should
be pretty quick, even for maximum batch size I think.
> although we could probably optimise
> > arm_smmu_cmdq_write_entries() into a memcpy() if we needed to.
> >
> > In other words, I think we need numbers to justify that change.
>
> Anyway, this is quite minor, and I will see if the change could be justified
> by numbers.
Thanks! If the numbers show it's useful, we can definitely add it.
Will
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next prev parent reply other threads:[~2019-07-24 14:07 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 17:19 [RFC PATCH v2 00/19] Try to reduce lock contention on the SMMUv3 command queue Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 01/19] iommu: Remove empty iommu_tlb_range_add() callback from iommu_ops Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 02/19] iommu/io-pgtable-arm: Remove redundant call to io_pgtable_tlb_sync() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 03/19] iommu/io-pgtable: Rename iommu_gather_ops to iommu_flush_ops Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 04/19] iommu: Introduce struct iommu_iotlb_gather for batching TLB flushes Will Deacon
2019-07-24 7:19 ` Joerg Roedel
2019-07-24 7:41 ` Will Deacon
2019-07-25 7:58 ` Joerg Roedel
2019-07-11 17:19 ` [RFC PATCH v2 05/19] iommu: Introduce iommu_iotlb_gather_add_page() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 06/19] iommu: Pass struct iommu_iotlb_gather to ->unmap() and ->iotlb_sync() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 07/19] iommu/io-pgtable: Introduce tlb_flush_walk() and tlb_flush_leaf() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 08/19] iommu/io-pgtable: Hook up ->tlb_flush_walk() and ->tlb_flush_leaf() in drivers Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 09/19] iommu/io-pgtable-arm: Call ->tlb_flush_walk() and ->tlb_flush_leaf() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 10/19] iommu/io-pgtable: Replace ->tlb_add_flush() with ->tlb_add_page() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 11/19] iommu/io-pgtable: Remove unused ->tlb_sync() callback Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 12/19] iommu/io-pgtable: Pass struct iommu_iotlb_gather to ->unmap() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 13/19] iommu/io-pgtable: Pass struct iommu_iotlb_gather to ->tlb_add_page() Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 14/19] iommu/arm-smmu-v3: Separate s/w and h/w views of prod and cons indexes Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 15/19] iommu/arm-smmu-v3: Drop unused 'q' argument from Q_OVF macro Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 16/19] iommu/arm-smmu-v3: Move low-level queue fields out of arm_smmu_queue Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 17/19] iommu/arm-smmu-v3: Operate directly on low-level queue where possible Will Deacon
2019-07-11 17:19 ` [RFC PATCH v2 18/19] iommu/arm-smmu-v3: Reduce contention during command-queue insertion Will Deacon
2019-07-19 11:04 ` John Garry
2019-07-24 12:15 ` Will Deacon
2019-07-24 14:03 ` John Garry
2019-07-24 14:07 ` Will Deacon [this message]
2019-07-24 8:20 ` John Garry
2019-07-24 14:33 ` Will Deacon
2019-07-25 11:31 ` John Garry
2019-07-11 17:19 ` [RFC PATCH v2 19/19] iommu/arm-smmu-v3: Defer TLB invalidation until ->iotlb_sync() Will Deacon
2019-07-19 4:25 ` [RFC PATCH v2 00/19] Try to reduce lock contention on the SMMUv3 command queue Ganapatrao Kulkarni
2019-07-24 12:28 ` Will Deacon
2019-07-24 9:58 ` John Garry
2019-07-24 12:20 ` Will Deacon
2019-07-24 14:25 ` John Garry
2019-07-24 14:48 ` Will Deacon
2019-07-25 10:11 ` John Garry
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