Re: USB transfer_buffer allocations on 64bit systems
From: Takashi Iwai
Date: Wed Apr 07 2010 - 14:06:16 EST
At Wed, 7 Apr 2010 19:59:35 +0200,
Daniel Mack wrote:
> On Wed, Apr 07, 2010 at 07:55:20PM +0200, Takashi Iwai wrote:
> > At Wed, 7 Apr 2010 18:16:03 +0200,
> > Daniel Mack wrote:
> > >
> > > On Wed, Apr 07, 2010 at 11:55:19AM -0400, Alan Stern wrote:
> > > > On Wed, 7 Apr 2010, Greg KH wrote:
> > > >
> > > > > Alan, any objection to just using usb_buffer_alloc() for every driver?
> > > > > Or is that too much overhead?
> > > >
> > > > I don't know what the overhead is. But usb_buffer_alloc() requires the
> > > > caller to keep track of the buffer's DMA address, so it's not a simple
> > > > plug-in replacement. In addition, the consistent memory that
> > > > usb_buffer_alloc() provides is a scarce resource on some platforms.
> > > >
> > > > Writing new functions is the way to go.
> > >
> > > Ok, I'll write some dummies for usb_malloc() and usb_zalloc() which
> > > will just call kmalloc() with GFP_DMA32 for now.
> > Can't we provide only zalloc() variant? Zero'ing doesn't cost much,
> > and the buffer allocation shouldn't be called too often.
> > > And while at it,
> > > usb_alloc_buffer() will be renamed to usb_alloc_consistent().
> > Most of recent functions are named with "coherent".
> I agree to both points, will do so unless anyone has a harsh opinion
> about that.
> Another thing: I guess we don't need a corresponding free() function
> that just calls kfree(), right? Or should we introduce it now to be
> flexible for future extensions?
Well, I would implement the corresponding free. It could be simply
a macro calling kfree(), but it's saner to provide it for API
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