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SubjectRe: [PATCH] 2.5.21 Nonlinear CPU support
Date
In message <20020611.021043.04190747.davem@redhat.com> you write:
> From: Rusty Russell <rusty@rustcorp.com.au>
> Date: Tue, 11 Jun 2002 19:09:44 +1000
>
> In message <3D05A9E8.FF0DA223@zip.com.au> you write:
> > and slowdown:
>
> 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(

I know *you* benchmark and read the asm during optimization, but it's
quite clear that others are so scared of "bloat" criticism that they
optimize without measuring the straightforward case *first*.

Remember, to be cool:
1) Use bitops and memory barriers not spinlocks,
2) Use inlines everywhere,
3) Use likely()/unlikely() on every branch
4) Use prefetch() everywhere,
5) Use gotos to minimize the path length
6) __set_current_state() not set_current_state()
7) Pass in current as a function param

Rusty.
--
Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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