[alsa-devel] USB transfer_buffer allocations on 64bit systems
stern at rowland.harvard.edu
Wed Apr 7 18:04:33 CEST 2010
On Wed, 7 Apr 2010, Greg KH wrote:
> > FWIW, most drivers I've seen in the past hours use a wild mix of
> > kmalloc(), kzalloc(), kcalloc() and usb_buffer_alloc(). That should
> > really be unified.
Well, kcalloc can easily be replaced by kzalloc, right? Or the
The extra overhead of initializing the memory to 0 isn't present in
kmalloc, so we need to maintain the distinction between kmalloc and
However usb_buffer_alloc is fundmentally different from all the others.
> Yes, if it is necessary that we have to handle this type of crappy
> hardware, then it all needs to be unified. Or at least unified into 2
> types of calls, one that needs the bounce buffer fun (what
> usb_buffer_alloc() does today), and one that doesn't (usb_kzalloc()
usb_buffer_alloc has very little to do with bounce buffers. Its
purpose is to allocate dma-consistent memory, that it, memory which
does not need to be mapped for DMA before each I/O operation and
The mapping and unmapping operations aren't extremely time consuming,
so in general it makes sense to avoid them only when the _same_ buffer
is going to be used for many I/O operations during a short period of
time. For instance, it makes sense for audio and video, where all the
data streams through a small set of buffers arranged in a ring.
But for most other uses it makes no sense. Especially since some
platforms have limited amounts of consistent memory available.
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