To: linux-kernel@vger.kernel.org
From: Kevin Puetz <puetzk@puetzk.org>
Subject: Re: [RFC] Splitting kernel headers and deprecating __KERNEL__
Date: Sun, 28 Nov 2004 10:34:46 -0600
Message-ID: <cocun6$e1g$1@sea.gmane.org>
References: <19865.1101395592@redhat.com> <200411272353.54056.arnd@arndb.de> <1101626019.2638.2.camel@laptop.fenrus.org> <200411281303.46609.arnd@arndb.de> <1101644385.2638.11.camel@laptop.fenrus.org>
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Arjan van de Ven wrote:

> implementing your own is still evil, but glibc provides similar
> constructs already. busy waiting in userspace is evil anyway (use futex
> :) and.... just as with atomic.h, spinlock.h only gets compiled in for
> CONFIG_SMP so the same caveats apply

Yeah, this is on it's way out now that futexes exist, but KDE (for one) used
to use spinlocks for a thread-pooled malloc (spin-sleep-spin-sleep though,
calling either sched_yield or nanosleep if the lock-grab failed - so it
wasn't a pure busy-wait). It didn't reuse spinlock.h from the kernel, but
it did use the general concept, since the old pre-futex posix mutexes were
crazy-slow for a lock which was heavily used but rarely contended.

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