linux-kernel - Re: [patch 05/11] syslets: core code

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Date:	Thu, 15 Feb 2007 00:44:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > case. (but with some crazier hacks i got the one-shot atom overhead 
> > [compared to a simple synchronous null syscall] to below 10 nsecs, 
> > so there's room in there for further optimizations. Our current null 
> > syscall latency is around ~150 nsecs.)
> 
> You are not counting the whole setup cost there, then, because your 
> setup cost is going to be at a minimum more expensive than the null 
> system call.

hm, this one-time cost was never on my radar. [ It's really dwarved by 
other startup costs (a single fork() takes 100 usecs, an exec() takes 
800 usecs.) ]

In any case, we can delay this cost into the first cachemiss, or can 
eliminate it by making it a globally pooled thing. It does not seem like 
a big issue.

	Ingo
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