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Message-Id: <20100125.154814.56026460.davem@davemloft.net>
Date: Mon, 25 Jan 2010 15:48:14 -0800 (PST)
From: David Miller <davem@...emloft.net>
To: shemminger@...tta.com
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH] tcp_probe: avoid modulus operation and wrap fix
From: Stephen Hemminger <shemminger@...tta.com>
Date: Mon, 25 Jan 2010 08:30:06 -0800
> On Sun, 24 Jan 2010 22:41:22 -0800 (PST)
> David Miller <davem@...emloft.net> wrote:
>
>> From: Stephen Hemminger <shemminger@...tta.com>
>> Date: Sun, 24 Jan 2010 21:50:01 -0800
>>
>> > @@ -75,12 +75,12 @@ static struct {
>> >
>> > static inline int tcp_probe_used(void)
>> > {
>> > - return (tcp_probe.head - tcp_probe.tail) % bufsize;
>> > + return (tcp_probe.head - tcp_probe.tail) & (bufsize - 1);
>> > }
>> >
>> > static inline int tcp_probe_avail(void)
>> > {
>> > - return bufsize - tcp_probe_used();
>> > + return bufsize - tcp_probe_used() - 1;
>> > }
>> >
>> > /*
>>
>> Hmmm... When the ring is full head==tail, which means
>> tcp_probe_used() returns 0. Which would now make tcp_probe_avail()
>> return "bufsize - 0 - 1".
>>
>> Is that right?
>
> Yes. in this ring; empty is head == tail, and full needs to
> be tail == head - 1.
Ok, that makes sense, thanks for explaining.
Applied, thanks Stephen.
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