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Message-ID: <4A830B8C.5000402@colorfullife.com>
Date: Wed, 12 Aug 2009 20:35:56 +0200
From: Manfred Spraul <manfred@colorfullife.com>
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To: Nick Piggin <npiggin@suse.de>
CC: Zach Brown <zach.brown@oracle.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Nadia Derbey <Nadia.Derbey@bull.net>,
       Pierre Peiffer <peifferp@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch 4/4] ipc: sem optimise simple operations
References: <20090811110902.255877673@suse.de> <20090811111607.310739140@suse.de> <4A81B646.5060301@colorfullife.com> <4A81B728.7040200@oracle.com> <20090812040756.GA5330@wotan.suse.de>
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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