linux-kernel - Re: [patch 4/4] ipc: sem optimise simple operations

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Message-ID: <4A830B8C.5000402@colorfullife.com>
Date:	Wed, 12 Aug 2009 20:35:56 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Nick Piggin <npiggin@...e.de>
CC:	Zach Brown <zach.brown@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nadia Derbey <Nadia.Derbey@...l.net>,
	Pierre Peiffer <peifferp@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 4/4] ipc: sem optimise simple operations

On 08/12/2009 06:07 AM, Nick Piggin wrote:
> A semaphore set with 250 will use 2K before, and 10K afterward. I
> don't know that it is a huge amount really, given that they also
> have to presumably be *protecting* stuff.
>
>    
The allocation uses vmalloc for larger allocations, thus 10k should not 
be an issue.
> We can convert them to hlists (I was going to send a patch to do
> everything in hlists, but hlists are missing some _rcu variants...
> maybe I should just convert the pending lists to start with).
>
>    
Is it possible to use list_add and list_add_tail instead?
Add the "waiting for zero" to the beginning and "waiting for nonzero" to 
the end.

Basically, the same approach for "simple" and "complex" operations:
- if all operations are simple operations, then all operations affect 
only individual semaphores
--> use per semaphore lists
- if there is one complex operation, then the global, per 
semaphore-array lists are used.


--
     Manfred
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