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Message-ID: <20080907060146.GB2244@1wt.eu>
Date: Sun, 7 Sep 2008 08:01:46 +0200
From: Willy Tarreau <w@....eu>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Alok Kataria <akataria@...are.com>,
Alan Cox <alan@...rguk.ukuu.org.uk>,
LKML <linux-kernel@...r.kernel.org>,
Arjan van de Veen <arjan@...radead.org>,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Dan Hecht <dhecht@...are.com>,
Garrett Smith <garrett@...are.com>
Subject: Re: [RFC patch 0/4] TSC calibration improvements
On Sat, Sep 06, 2008 at 02:10:32PM -0700, Linus Torvalds wrote:
> The fact is, the code that Ingo added was totally bogus. The real bug was
> that he did a totally bogus "--expect" in the argument to that last call.
BTW, I hate to see state-changing instructions inside an if condition.
I've been bitten several times while debugging. You try to temporarily
comment out the if statement for a test and you end up with different
code. Same for printf. Examples of dangerous usages :
i = 0;
for (x = 0; x < 100; x++) {
update_var(&i);
if (debug && i--)
printf("Hey I'm here\n");
}
return i;
You can bet that the if will go away before production. Variant with
similar effects :
i = 0;
for (x = 0; x < 100; x++) {
update_var(&i);
printf("Hey I'm here : %d\n", --i);
}
return i;
Since it costs nothing (except one tab and one LF) to put the instruction
out of the condition, I prefer to see them extracted :
i = 0;
for (x = 0; x < 100; x++) {
update_var(&i);
i--;
if (debug)
printf("Hey I'm here\n");
}
return i;
>
Willy
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