Date: Fri, 17 Sep 2004 08:43:21 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Bill Huey <bhuey@lnxw.com>
Cc: "David S. Miller" <davem@davemloft.net>, davidsen@tmr.com,
       linux-kernel@vger.kernel.org
Subject: Re: [patch] remove the BKL (Big Kernel Lock), this time for real
Message-ID: <20040917064321.GA8146@elte.hu>
References: <m3vfefa61l.fsf@averell.firstfloor.org> <cic7f9$i4m$1@gatekeeper.tmr.com> <20040916222903.GA4089@nietzsche.lynx.com> <20040916154011.3f0dbd54.davem@davemloft.net> <20040916225102.GA4386@nietzsche.lynx.com>
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* Bill Huey <bhuey@lnxw.com> wrote:

> Judging from how the Linux code is done and the numbers I get from
> Bill Irwin in casual conversation, the Linux SMP approach is clearly
> the right track at this time with it's hand honed per-CPU awareness of
> things. The only serious problem that spinlocks have as they aren't
> preemptable, which is what Ingo is trying to fix.

a clarification: note that the current BKL is a special case. No way do
i suggest that the BKS is the proper model for any SMP implementation.
It is a narrow special-case because it wraps historic UP-only kernel
code.

our primary multiprocessing primitives are still the following 4:
lockless data structures, RCU, spinlocks and mutexes. (reverse ordered
by level of parallelism.) The BKS is basically a fifth method, a special
type of semaphore that i'd never want to be seen used by any new SMP
code. It is completely local to sched.c.

	Ingo
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