linux-kernel - Re: [PATCH] v3 RCU: the bloatwatch edition

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Message-ID: <13990.1240928654@redhat.com>
Date:	Tue, 28 Apr 2009 15:24:14 +0100
From:	David Howells <dhowells@...hat.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	akpm@...ux-foundation.org, niv@...ibm.com, dvhltc@...ibm.com,
	lethal@...ux-sh.org, kernel@...tstofly.org, matthew@....cx
Subject: Re: [PATCH] v3 RCU: the bloatwatch edition

Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> This patch is a version of RCU designed for (!SMP && EMBEDDED)
> provided as a proof of concept of a small-footprint RCU implementation.
> In particular, the implementation of synchronize_rcu() is extremely
> lightweight and high performance.  It passes rcutorture testing in each
> of the four relevant configurations (combinations of NO_HZ and PREEMPT)
> on x86.  This saves about 900 bytes compared to Classic RCU, and a
> couple kilobytes compared to Hierarchical RCU:

On FRV, CLASSIC_RCU:

   text    data     bss     dec     hex filename
   2616     184       0    2800     af0 kernel/rcuclassic.o
    884      32      20     936     3a8 kernel/rcupdate.o

TREE_RCU:

   3940     328       0    4268    10ac kernel/rcutree.o
    884      32      20     936     3a8 kernel/rcupdate.o

TINY_RCU:

   1152      32       0    1184     4a0 kernel/rcutiny.o
    836      32      20     888     378 kernel/rcupdate.o

It works on my FRV board.

Possibly TINY_RCU could be shrunk a bit more by a judicious bit of inlining of
some of the very small functions.

Acked-by: David Howells <dhowells@...hat.com>
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