linux-kernel - Re: [PATCH 3/4] usb: allocated usb releated dma buffer with kmalloc

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Message-ID: <20070703060155.GB19086@kroah.com>
Date:	Mon, 2 Jul 2007 23:01:55 -0700
From:	Greg KH <greg@...ah.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	linux-usb-devel@...ts.sourceforge.net, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] usb: allocated usb releated dma buffer with
	kmalloc_node

On Mon, Jul 02, 2007 at 10:33:12PM -0700, Yinghai Lu wrote:
>  On 7/2/07, Greg KH <greg@...ah.com> wrote:
> > On Mon, Jul 02, 2007 at 03:36:37PM -0700, Yinghai Lu wrote:
> > > [PATCH 3/4] usb: allocated usb releated dma buffer with kmalloc_node
> > >
> > > For amd64 based two way system. USB always on node0. but dma buffer for 
> > urb
> > > allocated via kmalloc always get ram on node1. So change to kmalloc_node 
> > to
> > > get dma_buffer on corresponding node
> >
> > Are all of these changes really necessary?  You are doing this for some
> > allocations that take a _long_ time when sending to the device due to
> > the speed of the device.
> >
> > I could possibly see this making a difference on some drivers, but for
> > the core, and for the basic USB structures, I can't imagine it is really
> > worth it.
> >
> > Or do you have numbers showing the differences here?
> >
> > Patch included fully below for the benifit of the usb list, which you
> > should have cc:ed...
> 
>  dma buffer could be allocated via alloc_pages_coherent. or
>  kmalloc/dma_map_single.
>  alloc_pages_coherent get the dma_buffer on corresponding node.
>  but kmalloc/dma_map_single always get dma_buffer on last node. or say
>  device is on HT chain node0,  it will get dma buffer on node 7 of 8
>  socket system.
>  also on two way system with 4G+4G RAM conf. device on node 0 will get
>  dma_buffer above 4G, and if the dma_mask is less 32bit, will need
>  extra iommu mapping.
>  In my mcp55+io55 system, it show dma_map_single is keepping called by
>  usb input: keyboard/mouse (8/0x40 bytes), and forcedeth. (0x670bytes)

Ok, so two drivers might need this, but not the whole usb core, right?

And even if you do have another usb mapping, is that a real problem?
USB keyboards and mice are very slow.

thanks,

greg k-h
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