From: "Ray Lee" <ray-lk@madrabbit.org>
To: "pradeep singh rautela" <rautelap@gmail.com>
Cc: "Rusty Russell" <rusty@rustcorp.com.au>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
"Max Krasnyansky" <maxk@qualcomm.com>,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 5/5] tun: vringfd xmit support.
Date: Fri, 18 Apr 2008 07:25:27 -0700 [thread overview]
Message-ID: <2c0942db0804180725h88fa7d1mb8e85e5a8b0aede6@mail.gmail.com> (raw)
In-Reply-To: <6bc632150804180446u29e5dae9h986e1d255e584d21@mail.gmail.com>
On Fri, Apr 18, 2008 at 4:46 AM, pradeep singh rautela
<rautelap@gmail.com> wrote:
>
> On Fri, Apr 18, 2008 at 10:13 AM, Rusty Russell <rusty@rustcorp.com.au> wrote:
> > + /* How many pages will this take? */
> > + npages = 1 + (base + len - 1)/PAGE_SIZE - base/PAGE_SIZE;
>
> Hi Rusty,
> A trivial suggestion, how about
> npages = 1+(len -1)/PAGE_SIZE ?
That's not the same. In particular, his version accounts for the
fractional page at the beginning, while yours doesn't.
While it's tempting to use algebra to simplify things, it's not safe
to do so when the expression involves division over the integers. The
only care-free integer math in a computer is subtraction and ++.
next prev parent reply other threads:[~2008-04-18 14:25 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-18 4:33 [PATCH 0/5] High-speed tun receive and xmit Rusty Russell
2008-04-18 4:35 ` [PATCH 1/5] virtio: put last_used and last_avail index into ring itself Rusty Russell
2008-04-18 4:39 ` [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface Rusty Russell
2008-04-18 4:41 ` [PATCH 3/5] /dev/vring limit and base ioctls Rusty Russell
2008-04-18 4:42 ` [PATCH 4/5] tun: vringfd receive support Rusty Russell
2008-04-18 4:43 ` [PATCH 5/5] tun: vringfd xmit support Rusty Russell
2008-04-18 11:31 ` Andrew Morton
2008-04-18 15:15 ` Rusty Russell
2008-04-18 16:24 ` Ray Lee
2008-04-18 19:06 ` Andrew Morton
2008-04-19 14:41 ` Rusty Russell
2008-04-19 17:51 ` Andrew Morton
2008-04-19 1:54 ` Andrew Morton
2008-04-18 11:46 ` pradeep singh rautela
2008-04-18 14:25 ` Ray Lee [this message]
2008-04-18 18:01 ` pradeep singh rautela
2008-04-18 11:18 ` [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface Andrew Morton
2008-04-18 14:32 ` Rusty Russell
2008-04-18 18:59 ` Andrew Morton
2008-04-18 19:38 ` Michael Kerrisk
2008-04-19 16:41 ` Rusty Russell
2008-04-20 0:16 ` David Miller
2008-04-19 15:02 ` Jonathan Corbet
2008-04-19 10:22 ` Evgeniy Polyakov
2008-04-19 16:05 ` Rusty Russell
2008-04-19 16:33 ` Evgeniy Polyakov
2008-04-19 16:45 ` Rusty Russell
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