Date: Thu, 10 Nov 2005 22:02:55 +0100
From: Willy Tarreau <willy@w.ods.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Peter Staubach <staubach@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] poll(2) timeout values
Message-ID: <20051110210255.GF11266@alpha.home.local>
References: <437375DE.1070603@redhat.com> <1131642956.20099.39.camel@localhost.localdomain>
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On Thu, Nov 10, 2005 at 05:15:56PM +0000, Alan Cox wrote:
> On Iau, 2005-11-10 at 11:31 -0500, Peter Staubach wrote:
> > Clearly, the timeout calculations problem can be fixed without changing
> > the arguments to the sys_poll() routine.  However, it is cleaner to fix
> > it this way by ensuring the sizes and types of arguments match.
> 
> There really is no need for the kernel API to match the userspace one,
> many of our others differ between the syscall interface which is most
> definitely 'exported' in one sense and the POSIX interface which is
> defined by libc, posix and the LSB etc
> 
> No argument about the timeout fix.

I posted a different fix here about a month ago (but I sent it 3 times,
as it was twice wrong). Andrew was about to merge it in his tree but I
have not checked yet. It was different in the sense that it used
msecs_to_jiffies() to do the arithmetic in the best possible way depending
on the HZ value and the ints size. Most of the time (when 1000 % HZ == 0),
it will simplify the operations to a single divide by a constant and
correctly check for integer overflows. Eg, with HZ=250, a simple 2 bits
right shift will replace a multiply followed by an divide.

I'll check whether 2.6.14-mm1 has it, otherwise I can repost it.

Cheers,
Willy

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