From: Erik Andersen <andersen@codepoet.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Andrew Morton <akpm@osdl.org>,
"Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
linux-kernel@vger.kernel.org, jun.nakajima@intel.com
Subject: Re: [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take 2
Date: Sun, 31 Aug 2003 16:24:14 -0600 [thread overview]
Message-ID: <20030831222414.GA29923@codepoet.org> (raw)
In-Reply-To: <Pine.LNX.4.44.0308311404430.1581-100000@home.osdl.org>
On Sun Aug 31, 2003 at 02:05:25PM -0700, Linus Torvalds wrote:
>
> On Fri, 29 Aug 2003, Erik Andersen wrote:
> >
> > gcc then generates code calling __udivdi3 and __umoddi3. Since
> > the kernel does not provide these, people keep reinventing them.
> > Perhaps it is time to kill off do_div and all its little friends
> > and simply copy __udivdi3 and __umoddi3 from libgcc.....
>
> No. do_div() does _nothing_ like __udivdi3/__umoddi3.
>
> Read the documentation.
Been there done that, got the scars to prove it. do_div() is a
macro that acts sortof like the ISO C99 lldiv(3) function.
Except it does unexpected things like modify its arguments...
Most places in the kernel using do_div() not because it is the
right thing to do, but because they tried to do something
seemingly simple such as:
u64 foo, bar, baz;
...
baz = foo / bar;
and then got an error that __udivdi3 was undefined. So the
authors then go hunting for a way to do a 64 bit division and
find do_div()...
See mm/vmscan.c, mm/shmem.c, fs/proc/proc_misc.c,
drivers/ide/ide-disk.c, etc, etc, etc, for plenty of examples of
_exactly_ this sort of thing. Every one of them is using
do_div() to perform 64 bit division. Not becase that is the
right thing to do, but because __udivdi3 is missing.
-Erik
--
Erik B. Andersen http://codepoet-consulting.com/
--This message was written using 73% post-consumer electrons--
next prev parent reply other threads:[~2003-08-31 22:24 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-08-28 23:41 [PATCHSET][2.6-test4][0/6]Support for HPET based timer - Take 2 Pallipadi, Venkatesh
2003-08-29 18:23 ` Andrew Morton
2003-08-29 21:03 ` Erik Andersen
2003-08-31 21:05 ` Linus Torvalds
2003-08-31 22:24 ` Erik Andersen [this message]
2003-08-31 22:48 ` Linus Torvalds
2003-09-05 22:19 ` George Anzinger
[not found] <pEGJ.73p.5@gated-at.bofh.it>
2003-08-29 3:40 ` David Mosberger-Tang
2003-08-29 16:12 Pallipadi, Venkatesh
2003-08-30 4:59 ` David Mosberger-Tang
2003-08-29 23:58 Pallipadi, Venkatesh
2003-09-05 22:26 ` George Anzinger
2003-08-30 16:26 Pallipadi, Venkatesh
2003-09-06 19:04 Pallipadi, Venkatesh
2003-09-07 17:57 ` George Anzinger
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