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Message-Id: <201110191455.15540@zigzag.lvk.cs.msu.su> Date: Wed, 19 Oct 2011 14:55:13 +0400 From: "Nikita V. Youshchenko" <yoush@...msu.su> To: RKK <kulkarni.ravi4@...il.com> Cc: linux-kernel@...r.kernel.org, stefan@....cs.msu.su Subject: Re: high-order allocation + highmem + streaming DMA - possible? > > Hello. > > > > We are writing a driver for a custom PCI device that receives large > > amount of data. > > > > Device is capable of DMAing received data in 64k chunks. > > > > We have been going to: > > - use physically-continuous 64k-sized memory areas using alloc_pages() > > with order=4, > > - allocate large number of such areas on driver init, > > - implement mmap() to map those all to userspace for zero-copy > > processing, - use streaming DMA to actually receive data > > May i know why u want to mmap to userspace instead of using a > device? performance is affected by a large amount if u use mmap mmap() is done once, at initialization time, for entire data buffer. Later data is processed in zero-copy pattern. I believe it is fastest possible solution. > > Is there a way to use streaming DMA with large memory areas located in > > highmem? > > I dont think DMA is available for highmem? Not sure though . never saw > a usecase for it. DMA is definitly available for highmem on per-page basis. I'm interested in DMA of larger blocks. Nikita -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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