On Thursday 28 February 2002 00:29, Greg KH wrote:
> On Thu, Feb 28, 2002 at 12:18:41AM +0100, Oliver Neukum wrote:
> > Why ?
> > If the pool is formed by allocating the memory for urbs in chunks
> > the positive effect on TLB and cache is there whether the allocation
> > in the drivers is dynamic or not.
> > In fact, could we use the slab cache as is ?
>
> We could. But the point I was trying to make is that USB drivers only
> create urbs very infrequently (on device insertion), so any speed
> benefits are quite limited (we don't really care about speed when
> initializing a device.)
I must disagree partially.
The effect on TLB usage is the same whether the allocation
is dynamic or not. Furthermore we should plan for usb2.0
devices where it might be become noticeable.
AFAIK a Pentium class CPU has 16 entries for large pages.
This means that we can cache TLB entries for 64MB.
For my machine this makes a miss probability of 3/4
with randomly distributed urbs.
If we can't use large pages things become nasty.
USB on a 486 ?
Regards
Oliver
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