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

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Message-ID: <20121029190107.GD4066@htj.dyndns.org>
Date:	Mon, 29 Oct 2012 12:01:07 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Josh Triplett <josh@...htriplett.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paul.gortmaker@...driver.com, davem@...emloft.net,
	rostedt@...dmis.org, mingo@...e.hu, ebiederm@...ssion.com,
	aarcange@...hat.com, ericvh@...il.com, netdev@...r.kernel.org,
	eric.dumazet@...il.com, axboe@...nel.dk, agk@...hat.com,
	dm-devel@...hat.com, neilb@...e.de, ccaulfie@...hat.com,
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Subject: Re: [PATCH v7 06/16] tracepoint: use new hashtable implementation

On Mon, Oct 29, 2012 at 11:58:14AM -0700, Tejun Heo wrote:
> On Mon, Oct 29, 2012 at 02:53:19PM -0400, Mathieu Desnoyers wrote:
> > 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.

Thanks.

-- 
tejun
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