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

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Date:	Tue, 3 Jul 2007 00:03:12 -0700
From:	Greg KH <greg@...ah.com>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	linux-usb-devel@...ts.sourceforge.net,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: [linux-usb-devel] [PATCH 3/4] usb: allocated usb releated dma
	buffer with?kmalloc_node

On Tue, Jul 03, 2007 at 08:23:07AM +0200, Oliver Neukum wrote:
> Am Dienstag, 3. Juli 2007 schrieb Greg KH:
> > 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?
> 
> If those two drivers need the extended allocator, why not use it where
> it is beneficial, even if the benefit is small?

What is the benefit?  Speed isn't an issue here, so what is?

thanks,

greg k-h
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