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Date: Tue, 8 Jan 2013 07:31:30 -0700 From: Jonathan Corbet <corbet@....net> To: Marek Szyprowski <m.szyprowski@...sung.com> Cc: Mauro Carvalho Chehab <mchehab@...hat.com>, Alessandro Rubini <rubini@...dd.com>, federico.vaga@...il.com, mchehab@...radead.org, pawel@...iak.com, hans.verkuil@...co.com, giancarlo.asnaghi@...com, linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, s.nawrocki@...sung.com Subject: Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memory allocator On Tue, 08 Jan 2013 07:50:41 +0100 Marek Szyprowski <m.szyprowski@...sung.com> wrote: > > Couldn't this performance difference be due to the usage of GFP_DMA inside > > the VB2 code, like Federico's new patch series is proposing? > > > > If not, why are there a so large performance penalty? > > Nope, this was caused rather by a very poor CPU access to non-cached (aka > 'coherent') memory and the way the video data has been accessed/read > with CPU. Exactly. Uncached memory *hurts*, especially if you're having to touch it all with the CPU. jon -- 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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