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Date: Thu, 19 Dec 2002 00:53:27 +0100
From: Pavel Machek <pavel@ucw.cz>
To: dean gaudet <dean-list-linux-kernel@arctic.org>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       Dave Jones <davej@codemonkey.org.uk>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, hpa@transmeta.com
Subject: Re: Intel P6 vs P7 system call performance
Message-ID: <20021218235327.GC705@elf.ucw.cz>
References: <Pine.LNX.4.44.0212162204300.1800-100000@home.transmeta.com> <Pine.LNX.4.50.0212162241150.26163-100000@twinlark.arctic.org>
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Hi!

> > It's not as good as a pure user-mode solution using tsc could be, but
> > we've seen the kinds of complexities that has with multi-CPU systems, and
> > they are so painful that I suspect the sysenter approach is a lot more
> > palatable even if it doesn't allow for the absolute best theoretical
> > numbers.
> 
> don't many of the multi-CPU problems with tsc go away because you've got a
> per-cpu physical page for the vsyscall?
> 
> i.e. per-cpu tsc epoch and scaling can be set on that page.

Problem is that cpu's can randomly drift +/- 100 clocks or so... Not
nice at all.
								Pavel
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