Re: [PATCH v7 06/16] tracepoint: use new hashtable implementation

* Tejun Heo (tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org) wrote:

On Mon, Oct 29, 2012 at 11:58:14AM -0700, Tejun Heo wrote:

quoted

On Mon, Oct 29, 2012 at 02:53:19PM -0400, Mathieu Desnoyers wrote:

quoted

The argument about hash_init being useful to add magic values in the
future only works for the cases where a hash table is declared with
DECLARE_HASHTABLE(). It's completely pointless with DEFINE_HASHTABLE(),
because we could initialize any debugging variables from within
DEFINE_HASHTABLE().

You can do that with [0 .. HASH_SIZE - 1] initializer.

And in general, let's please try not to do optimizations which are
pointless.  Just stick to the usual semantics.  You have an abstract
data structure - invoke the initializer before using it.  Sure,
optimize it if it shows up somewhere.  And here, if we do the
initializers properly, it shouldn't cause any more actual overhead -
ie. DEFINE_HASHTABLE() will basicallly boil down to all zero
assignments and the compiler will put the whole thing in .bss anyway.

Yes, agreed. I was going too far in optimization land by proposing
assumptions on zeroed memory. All I actually really care about is that
we don't end up calling hash_init() on a statically defined (and thus
already initialized) hash table.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com