From: Davide Libenzi <davidel@xmailserver.org>
To: Alexander Viro <viro@math.psu.edu>
Cc: Jonathan Lundell <jlundell@pobox.com>, Jan Hubicka <jh@suse.cz>,
linux-kernel@vger.kernel.org,
user-mode-linux-user@lists.sourceforge.net,
Jeff Dike <jdike@karaya.com>, Andrea Arcangeli <andrea@suse.de>,
Linus Torvalds <torvalds@transmeta.com>
Subject: Re: user-mode port 0.44-2.4.7
Date: Tue, 24 Jul 2001 09:52:29 -0700 (PDT) [thread overview]
Message-ID: <XFMail.20010724095229.davidel@xmailserver.org> (raw)
In-Reply-To: <Pine.GSO.4.21.0107241203260.25475-100000@weyl.math.psu.edu>
On 24-Jul-2001 Alexander Viro wrote:
>
>
> On Tue, 24 Jul 2001, Davide Libenzi wrote:
>
>> I would not call, to pretend the compiler to issue memory loads every time it access
>> a variable, a nontrivial way.
>> It sounds pretty clear to me.
>
> You know, one of the nice things about C is that unless you abuse
> preprocessor, reading code doesn't require doing far lookups. Most
> of it can be read and understood with very little context. "Do it
> once when you declare a variable" goes against that and that's
> not a good thing.
Look, you're not going to request any kind of black magic over that variable.
You're simply telling the compiler the way it has to ( not ) optimize the code.
This is IMHO a declaration time issue.
Looking at this code :
while (jiffies < ...) {
...
}
the "natural" behaviour that a reader expects is that the "content" of the memory
pointed by jiffied is loaded and compared.
That content, not the content of a register loaded 100 asm instructions before the load.
If you like this code more :
for (;;) {
barrier();
if (jiffies >= ...)
break;
...
}
It's clear that a declaration like :
__locked_access__ struct pio {
int a, b, c;
};
for (;;) {
++a;
if (a > b && c < a)
...
}
sounds a "Bad Thing"(tm) even to me.
- Davide
next prev parent reply other threads:[~2001-07-24 16:50 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-23 5:08 user-mode port 0.44-2.4.7 Jeff Dike
2001-07-23 15:56 ` Andrea Arcangeli
2001-07-23 15:59 ` Andrea Arcangeli
2001-07-23 16:17 ` Andrea Arcangeli
2001-07-23 16:51 ` Andrea Arcangeli
2001-07-23 16:33 ` Linus Torvalds
2001-07-23 16:45 ` Andrea Arcangeli
2001-07-23 17:32 ` Linus Torvalds
2001-07-23 17:50 ` Andrea Arcangeli
2001-07-23 18:11 ` Linus Torvalds
2001-07-23 18:27 ` Andrea Arcangeli
2001-07-23 20:00 ` Linus Torvalds
2001-07-23 20:15 ` Jonathan Lundell
2001-07-23 22:51 ` Linus Torvalds
2001-07-24 3:45 ` Jonathan Lundell
2001-07-24 15:41 ` Davide Libenzi
2001-07-24 15:46 ` Alexander Viro
2001-07-24 16:01 ` Davide Libenzi
2001-07-24 16:08 ` Alexander Viro
2001-07-24 16:52 ` Davide Libenzi [this message]
2001-07-24 16:59 ` Linus Torvalds
2001-07-24 17:31 ` Davide Libenzi
2001-07-24 17:38 ` Linus Torvalds
2001-07-24 18:07 ` Anton Altaparmakov
2001-07-23 20:44 ` Chris Friesen
2001-07-23 21:11 ` Andrea Arcangeli
2001-07-23 21:50 ` Richard Gooch
2001-07-23 22:09 ` Andrea Arcangeli
2001-07-23 13:20 ` Rob Landley
2001-07-23 22:27 ` Andrea Arcangeli
2001-07-23 17:50 ` Rob Landley
2001-07-23 23:47 ` Richard Gooch
2001-07-24 0:04 ` Andrea Arcangeli
2001-07-24 9:02 ` Jan Hubicka
2001-07-24 15:35 ` Linus Torvalds
2001-07-24 16:04 ` Linus Torvalds
2001-07-25 22:49 ` Andrea Arcangeli
2001-07-25 23:16 ` Linus Torvalds
2001-07-25 23:37 ` Chris Friesen
2001-07-26 18:28 ` Jan Hubicka
2001-07-26 18:35 ` Alan Cox
2001-07-23 22:53 ` Linus Torvalds
2001-07-23 23:13 ` Alan Cox
2001-07-23 20:25 ` Jeff Dike
[not found] <no.id>
2001-07-23 20:57 ` Alan Cox
2001-07-23 21:14 ` Chris Friesen
2001-07-25 19:12 ` Alan Cox
2001-07-25 23:49 ` Alan Cox
2001-07-25 19:03 James W. Lake
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