netdev - Re: [PATCH 09/10] Change perturb

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Message-ID: <47015CD4.2040302@fatooh.org>
Date:	Mon, 01 Oct 2007 13:47:16 -0700
From:	Corey Hickey <bugfood-ml@...ooh.org>
To:	Patrick McHardy <kaber@...sh.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 09/10] Change perturb_period to unsigned.

Patrick McHardy wrote:
> Corey Hickey wrote:
>> perturb_period is currently a signed integer, but I can't see any good
>> reason why this is so--a negative perturbation period will add a timer
>> that expires in the past, causing constant perturbation, which makes
>> hashing useless.
>>
>> 	if (q->perturb_period) {
>> 		q->perturb_timer.expires = jiffies + q->perturb_period;
>> 		add_timer(&q->perturb_timer);
>> 	}
>>
>> Strictly speaking, this will break binary compatibility with older
>> versions of tc, but that ought not to be a problem because (a) there's
>> no valid use for a negative perturb_period, and (b) negative values
>> will be seen as high values (> INT_MAX), which don't work anyway.
>>
>> If perturb_period is too large, (perturb_period * HZ) will overflow the
>> size of an unsigned int and wrap around. So, check for thet and reject
>> values that are too high.
> 
> 
> Sounds reasonable.
> 
>> --- a/net/sched/sch_sfq.c
>> +++ b/net/sched/sch_sfq.c
>> @@ -74,6 +74,9 @@
>>  typedef unsigned int sfq_index;
>>  #define SFQ_MAX_DEPTH (UINT_MAX / 2 - 1)
>>  
>> +/* We don't want perturb_period * HZ to overflow an unsigned int. */
>> +#define SFQ_MAX_PERTURB (UINT_MAX / HZ)
> 
> 
> jiffies are unsigned long.

Hmm. You're right. It looks like my previous patch obviated the need for 
this part. I'll remove it.

-Corey
-
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