From: Ingo Molnar <mingo@elte.hu>
To: Arjan van de Ven <arjan@infradead.org>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
arjanvandeven@gmail.com, Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: x86: clean up smpboot.c's use of udelay+schedule
Date: Tue, 31 Jan 2012 15:30:23 +0100 [thread overview]
Message-ID: <20120131143022.GE13676@elte.hu> (raw)
In-Reply-To: <20120131053236.3f120f11@infradead.org>
* Arjan van de Ven <arjan@infradead.org> wrote:
> On Tue, 31 Jan 2012 13:43:41 +0100
> Ingo Molnar <mingo@elte.hu> wrote:
> > > + usleep_range(100, 200);
> >
> > I'm wondering whether we could shorten this delay to say 10
> > usecs and thus save 0.1 msecs (or more) from a typical SMP
> > bootup?
>
> doesn't matter really; [...]
It matters somewhat, especially if PeterZ's suggestion is used,
which is far more clean as well. The magic delays are not really
justified anymore.
> [...] bringing up a cpu is several orders more expensive (>
> 100msec in 3.2, in 3.3 this got optimized to maybe 30 msec)
> 0.1 msec is the least of anyone's worries at this point ;-)
It's 3% of the 30 msecs overhead.
> ( would be nice if this was a completion, but this is rather
> fragile code in general... at least not making it spin is an
> incremental improvement )
Completions arent hard to use and the scheduler should be up and
running at this stage already.
Thanks,
Ingo
prev parent reply other threads:[~2012-01-31 14:30 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-31 4:53 x86: clean up smpboot.c's use of udelay+schedule Arjan van de Ven
2012-01-31 12:43 ` Ingo Molnar
2012-01-31 12:47 ` Peter Zijlstra
2012-01-31 12:53 ` Ingo Molnar
2012-01-31 13:01 ` Peter Zijlstra
2012-02-02 0:33 ` Paul E. McKenney
2012-02-02 8:03 ` Srivatsa S. Bhat
2012-02-02 15:23 ` Paul E. McKenney
2012-02-03 17:32 ` Paul E. McKenney
2012-01-31 13:43 ` Arjan van de Ven
2012-01-31 13:32 ` Arjan van de Ven
2012-01-31 14:30 ` Ingo Molnar [this message]
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