From: Niklas Schnelle <schnelle@linux.ibm.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: Matthew Rosato <mjrosato@linux.ibm.com>,
Will Deacon <will@kernel.org>,
Wenjia Zhang <wenjia@linux.ibm.com>,
Robin Murphy <robin.murphy@arm.com>,
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Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
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<angelogioacchino.delregno@collabora.com>,
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Thierry Reding <thierry.reding@gmail.com>,
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Jonathan Hunter <jonathanh@nvidia.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-s390@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
asahi@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
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Subject: Re: [PATCH v9 6/6] iommu/dma: Make flush queue sizes and timeout driver configurable
Date: Tue, 23 May 2023 14:20:24 +0200 [thread overview]
Message-ID: <b06a47fecf5eab9440c1c35d9c7b83fe87f918a0.camel@linux.ibm.com> (raw)
In-Reply-To: <ZGuT2R42SWFHmklu@8bytes.org>
On Mon, 2023-05-22 at 18:10 +0200, Joerg Roedel wrote:
> On Mon, May 15, 2023 at 11:15:56AM +0200, Niklas Schnelle wrote:
> > In the s390 IOMMU driver a large fixed queue size and timeout is then
> > set together with single queue mode bringing its performance on s390
> > paged memory guests on par with the previous s390 specific DMA API
> > implementation.
>
> Hmm, the right flush-queue size and timeout settings are more a function
> of the endpoint device and device driver than of the iommu driver, no? I
> think something like this could also help solving the recently reported
> scalability problems in the fq-code, if done right.
>
> Regards,
>
> Joerg
>
In our case the large flush queue and timeout is needed because the
IOTLB flushes of the virtualized s390 IOMMU are used by KVM and z/VM to
synchronize their IOMMU shadow tables thus making them more expensive.
This then applies to all pass-through PCI devices without their drivers
knowing about the IOMMU being virtualized like that. But yes of course
there could be cases where the device driver knows better.
Thanks,
Niklas
prev parent reply other threads:[~2023-05-23 12:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-15 9:15 [PATCH v9 0/6] iommu/dma: s390 DMA API conversion and optimized IOTLB flushing Niklas Schnelle
2023-05-15 9:15 ` [PATCH v9 1/6] s390/ism: Set DMA coherent mask Niklas Schnelle
2023-05-16 7:39 ` Pierre Morel
2023-05-16 7:58 ` Petr Tesařík
2023-05-15 9:15 ` [PATCH v9 2/6] iommu: Allow .iotlb_sync_map to fail and handle s390's -ENOMEM return Niklas Schnelle
2023-05-15 9:15 ` [PATCH v9 3/6] s390/pci: prepare is_passed_through() for dma-iommu Niklas Schnelle
2023-05-15 9:15 ` [PATCH v9 4/6] s390/pci: Use dma-iommu layer Niklas Schnelle
2023-05-15 9:15 ` [PATCH v9 5/6] iommu/dma: Allow a single FQ in addition to per-CPU FQs Niklas Schnelle
2023-05-15 13:07 ` Jason Gunthorpe
2023-05-15 14:42 ` Niklas Schnelle
2023-05-22 16:26 ` Robin Murphy
2023-05-23 12:02 ` Niklas Schnelle
2023-05-23 12:16 ` Robin Murphy
2023-05-23 13:35 ` Niklas Schnelle
2023-05-15 9:15 ` [PATCH v9 6/6] iommu/dma: Make flush queue sizes and timeout driver configurable Niklas Schnelle
2023-05-22 16:10 ` Joerg Roedel
2023-05-23 12:20 ` Niklas Schnelle [this message]
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