From: Grant Grundler <grantgrundler@gmail.com>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Christoph Hellwig <hch@lst.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
axboe@kernel.dk, dan.j.williams@intel.com, vgupta@synopsys.com,
hskinnemoen@gmail.com, egtvedt@samfundet.no, realmz6@gmail.com,
dhowells@redhat.com, monstr@monstr.eu, x86@kernel.org,
David Woodhouse <dwmw2@infradead.org>,
alex.williamson@redhat.com,
Grant Grundler <grundler@parisc-linux.org>,
open list <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, linux-alpha@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-metag@vger.kernel.org,
linux-mips@linux-mips.org,
linux-parisc <linux-parisc@vger.kernel.org>,
linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
linux-nvdimm@ml01.01.org, linux-media@vger.kernel.org
Subject: Re: RFC: prepare for struct scatterlist entries without page backing
Date: Wed, 12 Aug 2015 10:56:26 -0700 [thread overview]
Message-ID: <CAP6odjhfTHzgEivDUxXyU=VBG4U85ETxv1gcogE9GVGoGQ37-w@mail.gmail.com> (raw)
In-Reply-To: <1439398807.2825.51.camel@HansenPartnership.com>
On Wed, Aug 12, 2015 at 10:00 AM, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
> On Wed, 2015-08-12 at 09:05 +0200, Christoph Hellwig wrote:
...
>> However the ccio (parisc) and sba_iommu (parisc & ia64) IOMMUs seem
>> to be operate mostly on virtual addresses. It's a fairly odd concept
>> that I don't fully grasp, so I'll need some help with those if we want
>> to bring this forward.
James explained the primary function of IOMMUs on parisc (DMA-Cache
coherency) much better than I ever could.
Three more observations:
1) the IOMMU can be bypassed by 64-bit DMA devices on IA64.
2) IOMMU enables 32-bit DMA devices to reach > 32-bit physical memory
and thus avoiding bounce buffers. parisc and older IA-64 have some
32-bit PCI devices - e.g. IDE boot HDD.
3) IOMMU acts as a proxy for IO devices by fetching cachelines of data
for PA-RISC systems whose memory controllers ONLY serve cacheline
sized transactions. ie. 32-bit DMA results in the IOMMU fetching the
cacheline and updating just the 32-bits in a DMA cache coherent
fashion.
Bonus thought:
4) IOMMU can improve DMA performance in some cases using "hints"
provided by the OS (e.g. prefetching DMA data or using READ_CURRENT
bus transactions instead of normal memory fetches.)
cheers,
grant
prev parent reply other threads:[~2015-08-12 17:56 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-12 7:05 RFC: prepare for struct scatterlist entries without page backing Christoph Hellwig
2015-08-12 7:05 ` [PATCH 01/31] scatterlist: add sg_pfn and sg_has_page helpers Christoph Hellwig
2015-08-12 7:05 ` [PATCH 02/31] scatterlist: use sg_phys() Christoph Hellwig
2015-08-12 7:05 ` [PATCH 03/31] dma-debug: handle page-less SG entries Christoph Hellwig
2015-08-12 7:05 ` [PATCH 04/31] x86/pci-nommu: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 05/31] x86/pci-calgary: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 06/31] alpha/pci-noop: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 07/31] alpha/pci_iommu: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 08/31] c6x: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 09/31] ia64/pci_dma: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 10/31] powerpc/iommu: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 11/31] sparc/iommu: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 12/31] mn10300: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 13/31] sparc/ldc: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 14/31] sparc32/io-unit: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 15/31] sparc32/iommu: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 16/31] s390: " Christoph Hellwig
2015-08-12 11:51 ` Sebastian Ott
2015-08-12 7:05 ` [PATCH 17/31] ia64/sba_iommu: remove sba_sg_address Christoph Hellwig
2015-08-12 7:05 ` [PATCH 18/31] nios2: handle page-less SG entries Christoph Hellwig
2015-08-12 7:05 ` [PATCH 19/31] arc: " Christoph Hellwig
2015-08-12 10:28 ` Vineet Gupta
2015-08-12 7:05 ` [PATCH 20/31] avr32: " Christoph Hellwig
2015-08-12 9:36 ` Hans-Christian Egtvedt
2015-08-12 7:05 ` [PATCH 21/31] blackfin: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 22/31] metag: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 23/31] sh: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 24/31] xtensa: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 25/31] frv: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 26/31] openrisc: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 27/31] mips: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 28/31] powerpc: " Christoph Hellwig
2015-08-12 7:05 ` [PATCH 29/31] parisc: " Christoph Hellwig
2015-08-12 16:01 ` Linus Torvalds
2015-08-13 14:31 ` Christoph Hellwig
2015-08-14 3:30 ` Dan Williams
2015-08-14 3:59 ` James Bottomley
2015-08-14 4:11 ` David Miller
2015-08-14 16:17 ` Dan Williams
2015-08-12 7:05 ` [PATCH 30/31] intel-iommu: " Christoph Hellwig
2015-08-12 9:51 ` David Woodhouse
2015-08-12 7:05 ` [PATCH 31/31] dma-mapping-common: skip kmemleak checks for " Christoph Hellwig
2015-08-12 16:05 ` Linus Torvalds
2015-08-13 14:33 ` Christoph Hellwig
2015-08-12 16:26 ` Catalin Marinas
2015-08-12 12:42 ` RFC: prepare for struct scatterlist entries without page backing Boaz Harrosh
2015-08-12 23:37 ` Julian Calaby
2015-08-13 14:35 ` Christoph Hellwig
2015-08-13 23:40 ` Julian Calaby
2015-08-13 14:40 ` Christoph Hellwig
2015-08-13 15:42 ` Boaz Harrosh
2015-08-12 17:00 ` James Bottomley
2015-08-12 17:56 ` Grant Grundler [this message]
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