linux.conf.au
Optimization

From: Rusty Russell <rusty@rustcorp.com.au>
To: "David S. Miller" <davem@redhat.com>
Cc: akpm@zip.com.au, torvalds@transmeta.com, linux-kernel@vger.kernel.org, k-suganuma@mvj.biglobe.ne.jp
Subject: Re: [PATCH] 2.5.21 Nonlinear CPU support 

In message <20020611.021043.04190747.davem@redhat.com> you write:
>    ARGH!  STOP IT!  I realize it's 'leet to be continually worrying about
>    possible microoptimizations, but I challenge you to *measure* the
>    slowdown between:
> 
> Regardless, his space arguments still hold.

 	You can allocate based on cpu_possible(cpu) (which is in the
next patch) if you like, but I think you're better off fixing the
existing NR_CPUS bloat as well, and keeping all the code simple.

> I don't like having everyone eat the overhead that hotplugging cpus
> seem to entail.

 	But there's an important difference between something which is
simple and unoptimized, and something which is unoptimizable.

> And remember, it's the anal "every microoptimization at all costs"
> people that keep the kernel sane and from running out of control bloat
> wise.

But it also gave us crap like net/ipv4/route.c:ip_rt_acct_read() 8(