On Thu, 6 Oct 2005, Hugh Dickins wrote:
>
> That reminds me: ought cond_resched_lock to be doing something more?
I suspect the "need_resched()" case is sufficient in practice: it might
not be perfect, but let's face it, there's not a lot we can do.
It's true that the cpu_relax() basically does nothing except perhaps by
luck (and depending on CPU and memory setup). There's no good alternative,
though. You could make it more complex and change the cpu_relax() to
something like
i = random_backoff();
for (;;) {
cpu_relax();
if (spin_is_locked(lock))
break;
if (!need_lockbreak(lock))
break;
if (!--i)
break;
}
but I'd argue vehemently that you shouldn't do this unless you can see
real problems.
I doubt it's really a problem in practice. You have to have a really hot
spinlock that stays hot on one CPU (and most of them you can't even _make_
hot from user space), and I suspect we've fixed the ones that matter.
Linus
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