netdev - Re: [PATCH] iproute2: Avoid rounding errors for 100%.

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Date:	Tue, 03 Nov 2009 18:19:19 +0100
From:	Arnd Hannemann <hannemann@...s.rwth-aachen.de>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] iproute2: Avoid rounding errors for 100%.

Stephen Hemminger wrote:
> On Tue, 03 Nov 2009 17:19:45 +0100
> Arnd Hannemann <hannemann@...s.rwth-aachen.de> wrote:
> 
>> Although the patch makes sense,
>> it does not fix the bug/effect we were seeing.
>> A netem reorder percentage of 100% will still get packets reordered.
>> (if the netem queue is not empty)
>>
>>
>> hannemann@...s.rwth-aachen.de wrote:
>>> From: Arnd Hannemann <hannemann@...s.rwth-aachen.de>
>>>
>>> We noticed that a netem reorder percentage of 100% will still get packets reordered.
>>> This patch fixes that.
>>>
>>> Signed-off-by: Arnd Hannemann <hannemann@...s.rwth-aachen.de>
>>> ---
>>>  tc/tc_util.c |    6 ++++--
>>>  1 files changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tc/tc_util.c b/tc/tc_util.c
>>> index fe2c7eb..2641f2e 100644
>>> --- a/tc/tc_util.c
>>> +++ b/tc/tc_util.c
>>> @@ -363,8 +363,10 @@ int get_percent(__u32 *percent, const char *str)
>>>  		return -1;
>>>  	if (*p && strcmp(p, "%"))
>>>  		return -1;
>>> -
>>> -	*percent = (unsigned) rint(per * max_percent_value);
>>> +	if (per == 1.)
>>> +		*percent = max_percent_value;
>>> +	else
>>> +		*percent = (unsigned) rint(per * max_percent_value);
>>>  	return 0;
>>>  }
>>>  
>>
> 
> If you don't want reordering, don't specify reordering?

Are you arguing against the correctness of my patch?

Regarding, the reordering thingy/bug/effect whatever:
We would like to specify reordering with something like this:
Please delay 1% of the packets with 5ms.

We thought that would be possible with
tc qdisc add dev eth0 root netem delay 5m reorder 99%

But unfortunately it is not. Any better idea?

Best regards,
Arnd
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