Re: USB transfer_buffer allocations on 64bit systems

From: Takashi Iwai
Date: Wed Apr 07 2010 - 13:55:25 EST

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".


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