linux-kernel - Re: Plumbers: Tweaking scheduler policy micro-conf RFP

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Date:	Wed, 23 May 2012 17:50:03 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Chen <hi3766691@...il.com>, Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: Plumbers: Tweaking scheduler policy micro-conf RFP


* Joe Perches <joe@...ches.com> wrote:

> On Wed, 2012-05-23 at 17:03 +0200, Ingo Molnar wrote:
> > * Chen <hi3766691@...il.com> wrote:
> > 
> > > Still you are just trying to said that your code is not bloated?
> > > Up to over 500K for a cpu scheduler. Laughing
> > 
> > Where did you get that 500K from? You are off from the truth 
> > almost by an order of magnitude.
> > 
> > Here's the scheduler size on Linus's latest tree, on 64-bit 
> > defconfig's:
> > 
> >  $ size kernel/sched/built-in.o 
> >    text	   data	    bss	    dec	    hex	filename
> >   83611	  10404	   2524	  96539	  1791b	kernel/sched/built-in.o
> > 
> > That's SMP+NUMA, i.e. everything included.
> > 
> > The !NUMA !SMP UP scheduler, if you are on a size starved 
> > ultra-embedded device, is even smaller, just 22K:
> > 
> >  $ size kernel/sched/built-in.o 
> >    text	   data	    bss	    dec	    hex	filename
> >   19882	   2218	    148	  22248	   56e8	kernel/sched/built-in.o
> 
> Here's an allyesconfig x86-32

allyesconfig includes a whole lot of debugging code so it's a 
pretty meaningless size test.

> $ size kernel/sched/built-in.o
>    text	   data	    bss	    dec	    hex	filename
>  213892	  10856	  65832	 290580	  46f14	kernel/sched/built-in.o
> 
> But that's not the only sched related code.
> 
> In a 1000 cpu config, there also an extra 500+ bytes per cpu
> in printk (I don't think that's particularly important btw)

A 1000 cpu piece of hardware will have a terabyte of RAM or 
more. 0.5K per CPU is reasonable.

> kernel/printk.c adds:
> 
> static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf);
> 
> Maybe #ifdefing this when !CONFIG_PRINTK would reduce size
> a little in a few cases.  I've attached a trivial suggested patch.

That might make sense for the ultra-embedded.

Still 500K is an obviously nonsensical number.

Thanks,

	Ingo
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