linux-kernel - Re: x86: clean up smpboot.c's use of udelay+schedule

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120131143022.GE13676@elte.hu>
Date:	Tue, 31 Jan 2012 15:30:23 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	arjanvandeven@...il.com, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: x86: clean up smpboot.c's use of udelay+schedule


* Arjan van de Ven <arjan@...radead.org> wrote:

> On Tue, 31 Jan 2012 13:43:41 +0100
> Ingo Molnar <mingo@...e.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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/