Re: [PATCH 00/16] Remove the ipv4 routing cache

[Eric Dumazet <eric.dumazet@gmail.com>]

On Fri, 2012-07-27 at 07:53 -0700, Eric W. Biederman wrote:
> Eric Dumazet <eric.dumazet@gmail.com> writes:
> 
> > Now IP route cache is removed, we should make sure fib structures
> > cant share cache lines with possibly often dirtied objects.
> >
> > On x86, kmalloc-96 cache can be source of such problems.
> >
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> 
> 
> > +static inline void *fib_zalloc(size_t size)
> > +{
> > +	/* We want to avoid possible false sharing */
> > +	return kzalloc(max_t(size_t, 128, size), GFP_KERNEL);
> 
> Why the hard coded 128 here?
> 
> It seems more portable and obvious to do 
> 	return kzalloc(round_up(size, L1_CACHE_BYTES), GFP_KERNEL);
> 

Its not that obvious, because some machines have an apparent
L1_CACHE_BYTES of 64, but hardware prefetching to 128 bytes

But using 2*L1_CACHE_BYTES as minimum allocation size might be overkill
on some arches with 256 bytes cache lines.