linux-kernel - Re: [PATCH 2/2] ioatdma: add DMA

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Message-ID: <84A937D219C2B44EB8EA44831ACA1E4917266843@PRN-MBX01-3.TheFacebook.com>
Date:	Thu, 27 Jun 2013 01:10:58 +0000
From:	Dan Williams <djbw@...com>
To:	Jon Mason <jon.mason@...el.com>
CC:	Vinod Koul <vinod.koul@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ioatdma: add DMA_PRIVATE capabilities flag



On 6/26/13 4:55 PM, "Jon Mason" <jon.mason@...el.com> wrote:
>Unfortunately, the dma_find_channel model does not led itself to
>optimal usage of the available channels, as it seems to give out the
>same channel.  Adding some randomizer (or other way to spread the
>channel selection over multiple channels) would be greatly
>beneficial.

Right now the allocation scheme is per-cpu.  If you have multiple
submission contexts on different cpus it should use all available channels.

>Alternatively, adding an async_memcpy_mmio function (and perhaps some
>minimal size to use the DMA engine) would provide a solution that
>would work.

It¹s hard.  The size is arch and use specific so it may be best to leave
it up to the client.

>However, dma_find_channel should be sufficient to get NTB use of DMA
>engines out for review.  I'll clean it up and send it out shortly.
>Thanks for the insight.

Cool, I¹ll take a look.


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