From: Bjorn Helgaas <bhelgaas@google.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
linux-doc@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Joerg Roedel <joro@8bytes.org>,
Randy Dunlap <rdunlap@infradead.org>,
Liviu Dudau <Liviu.Dudau@arm.com>,
linux-kernel@vger.kernel.org,
James Bottomley <jbottomley@parallels.com>,
linux-pci@vger.kernel.org
Subject: Re: [PATCH v2 4/5] iommu: Use dma_addr_t for IOVA arguments
Date: Fri, 9 May 2014 09:32:26 -0600 [thread overview]
Message-ID: <20140509153226.GA3571@google.com> (raw)
In-Reply-To: <1399629530.879.21.camel@i7.infradead.org>
On Fri, May 09, 2014 at 10:58:50AM +0100, David Woodhouse wrote:
> On Thu, 2014-05-08 at 14:30 -0600, Bjorn Helgaas wrote:
> > I doubt there would be a noticeable performance effect since these are
> > relatively low-frequency interfaces (map, unmap, report_fault),
>
> That point of view makes me sad.
Don't be sad; Arnd successfully fended off the challenge :)
> There are people who care deeply about the performance of IOMMU API
> map/unmap. It isn't used *just* for virtual machines any more. See
> drivers/infiniband/hw/usnic/usnic_uiom.c for example.
Of course we should care about IOMMU API performance. We should also
care about interface consistency, and it seems there's a tradeoff in
this case. I said "relatively" because I expect map/unmap to be less
frequent than read/write operations that use the mapping. I don't
know anything about infiniband, so maybe that assumption is false
there.
> I also hold out *some* hope for consolidating the map/unmap functions
> for the IOMMU and DMA APIs at some point. The main difference is that
> the DMA API allocates an IOVA for itself, while the IOMMU API is given
> the bus address too.
I find this aspect of these APIs confusing, so I agree that it would
be nice if these could be consolidated somehow.
Bjorn
next prev parent reply other threads:[~2014-05-09 15:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-06 22:48 [PATCH v2 0/5] Clean up DMA API & IOMMU dma_addr_t usage Bjorn Helgaas
2014-05-06 22:48 ` [PATCH v2 1/5] DMA-API: Clarify physical/bus address distinction Bjorn Helgaas
2014-05-07 7:37 ` Arnd Bergmann
2014-05-07 18:43 ` Bjorn Helgaas
2014-05-08 9:24 ` Greg Kroah-Hartman
2014-05-06 22:48 ` [PATCH v2 2/5] DMA-API: Change dma_declare_coherent_memory() CPU address to phys_addr_t Bjorn Helgaas
2014-05-07 7:38 ` Arnd Bergmann
2014-05-06 22:48 ` [PATCH v2 3/5] sh/PCI: Pass GAPSPCI_DMA_BASE CPU address to dma_declare_coherent_memory() Bjorn Helgaas
2014-05-07 7:55 ` Arnd Bergmann
2014-05-07 8:15 ` Arnd Bergmann
2014-05-07 23:18 ` Bjorn Helgaas
2014-05-08 11:36 ` Arnd Bergmann
2014-05-06 22:48 ` [PATCH v2 4/5] iommu: Use dma_addr_t for IOVA arguments Bjorn Helgaas
2014-05-07 7:58 ` Arnd Bergmann
2014-05-08 0:18 ` Bjorn Helgaas
2014-05-08 10:44 ` Arnd Bergmann
2014-05-08 20:30 ` Bjorn Helgaas
2014-05-09 9:58 ` David Woodhouse
2014-05-09 15:32 ` Bjorn Helgaas [this message]
2014-05-09 19:52 ` Arnd Bergmann
2014-05-09 20:19 ` Bjorn Helgaas
2014-05-09 20:25 ` James Bottomley
2014-05-06 22:48 ` [PATCH v2 5/5] iommu/exynos: Remove unnecessary "&" from function pointers Bjorn Helgaas
2014-05-07 7:59 ` Arnd Bergmann
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