linux-kernel - Re: [PATCH] v5 RCU: the bloatwatch edition

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Message-ID: <20090623125832.GA6872@linux.vnet.ibm.com>
Date:	Tue, 23 Jun 2009 05:58:32 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Howells <dhowells@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, niv@...ibm.com, dvhltc@...ibm.com,
	lethal@...ux-sh.org, kernel@...tstofly.org, matthew@....cx
Subject: Re: [PATCH] v5 RCU: the bloatwatch edition

On Tue, Jun 23, 2009 at 11:32:08AM +0200, Ingo Molnar wrote:
> 
> * David Howells <dhowells@...hat.com> wrote:
> 
> > 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 1263 bytes compared to Classic RCU, and more than
> > > three kilobytes compared to Hierarchical RCU (updated to 2.6.30):
> > 
> > On FRV:
> > 
> > 	CONFIG_CLASSIC_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    884      32      20     936     3a8 kernel/rcupdate.o
> > 	   2616     184       0    2800     af0 kernel/rcuclassic.o
> > 
> > 	CONFIG_TREE_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    884      32      20     936     3a8 kernel/rcupdate.o
> > 	   4068     384       0    4452    1164 kernel/rcutree.o
> > 
> > 	CONFIG_TINY_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    836      32      20     888     378 kernel/rcupdate.o
> > 	    816      24       0     840     348 kernel/rcutiny.o
> > 
> > On MN10300:
> > 
> > 	CONFIG_CLASSIC_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    900      28      48     976     3d0 kernel/rcupdate.o
> > 	   1777     184       0    1961     7a9 kernel/rcuclassic.o
> > 
> > 	CONFIG_TREE_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    900      28      48     976     3d0 kernel/rcupdate.o
> > 	   2733     384       0    3117     c2d kernel/rcutree.o
> > 
> > 	CONFIG_PREEMPT_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    961      28      48    1037     40d kernel/rcupdate.o
> > 	   3314     128       8    3450     d7a kernel/rcupreempt.o
> > 
> > 	CONFIG_TINY_RCU=y
> > 
> > 	   text    data     bss     dec     hex filename
> > 	    865      28      48     941     3ad kernel/rcupdate.o
> > 	    500      24       0     524     20c kernel/rcutiny.o
> > 
> > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > Acked-by: David Howells <dhowells@...hat.com
> 
> Ok, that's more convincing than 900 bytes on x86.

It used to be 900 bytes.  In 2.6.30, it is 1263 bytes.  ;-)

That said, I agree that FRV and MN10300 savings are more impressive.

> Paul, i guess this is .32 material anyway, right?

I am personally OK with it being .32, as long as David Howells,
Lennert Buytenhek, and Paul Mundt are OK with that schedule.

> Since there's plenty of time, could we perhaps also do the 
> classic-rcu removal and integrate-rcupreempt-into-tree-rcu steps, to 
> reduce the (significant) config complexity perhaps?

Classic-RCU removal most certainly.  I am hoping to get the
integrate-rcupreempt-into-tree-rcu piece done in .32 timeframe, but
there is a chance that it may be a bit later.

							Thanx, Paul
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