netdev - Re: weird problem

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Date:	Fri, 10 Jul 2009 01:14:20 +0200
From:	Paweł Staszewski <pstaszewski@...are.pl>
To:	Jarek Poplawski <jarkao2@...il.com>
CC:	Eric Dumazet <dada1@...mosbay.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Network Development list <netdev@...r.kernel.org>
Subject: Re: weird problem

Jarek Poplawski pisze:
> Pawel Staszewski wrote, On 06/30/2009 10:36 AM:
> ...
>   
>>>>>> rt_worker_func() taking 13% of cpu0 is an alarm for me :)
>>>>>> And 21% of cpu0 and 34% of cpu6 taken by oprofiled seems odd too...
>>>>>>             
>
> Pawel, here is a patch which changes this function (or what it calls)
> back to 2.6.28 version; I'm not sure it's OK, so try it very
> cautiously...
>
> Cheers,
> Jarek P.
> --- (for debugging only; apply to 2.6.29.5 or .6)
>
>   
I added this patch 30min ago - all is working but problem still exist.

There is only one change - without this patch cpu load was rising from 
40 to 50%
With this patch there is 15 to 25% cpu load.


> diff -Nurp a/net/ipv4/route.c b/net/ipv4/route.c
> --- a/net/ipv4/route.c	2009-07-08 23:42:15.000000000 +0200
> +++ b/net/ipv4/route.c	2009-07-08 22:47:52.000000000 +0200
> @@ -769,24 +769,11 @@ static void rt_do_flush(int process_cont
>  	}
>  }
>  
> -/*
> - * While freeing expired entries, we compute average chain length
> - * and standard deviation, using fixed-point arithmetic.
> - * This to have an estimation of rt_chain_length_max
> - *  rt_chain_length_max = max(elasticity, AVG + 4*SD)
> - * We use 3 bits for frational part, and 29 (or 61) for magnitude.
> - */
> -
> -#define FRACT_BITS 3
> -#define ONE (1UL << FRACT_BITS)
> -
>  static void rt_check_expire(void)
>  {
>  	static unsigned int rover;
>  	unsigned int i = rover, goal;
> -	struct rtable *rth, *aux, **rthp;
> -	unsigned long samples = 0;
> -	unsigned long sum = 0, sum2 = 0;
> +	struct rtable *rth, **rthp;
>  	u64 mult;
>  
>  	mult = ((u64)ip_rt_gc_interval) << rt_hash_log;
> @@ -797,7 +784,6 @@ static void rt_check_expire(void)
>  		goal = rt_hash_mask + 1;
>  	for (; goal > 0; goal--) {
>  		unsigned long tmo = ip_rt_gc_timeout;
> -		unsigned long length;
>  
>  		i = (i + 1) & rt_hash_mask;
>  		rthp = &rt_hash_table[i].chain;
> @@ -805,14 +791,10 @@ static void rt_check_expire(void)
>  		if (need_resched())
>  			cond_resched();
>  
> -		samples++;
> -
>  		if (*rthp == NULL)
>  			continue;
> -		length = 0;
>  		spin_lock_bh(rt_hash_lock_addr(i));
>  		while ((rth = *rthp) != NULL) {
> -			prefetch(rth->u.dst.rt_next);
>  			if (rt_is_expired(rth)) {
>  				*rthp = rth->u.dst.rt_next;
>  				rt_free(rth);
> @@ -821,46 +803,23 @@ static void rt_check_expire(void)
>  			if (rth->u.dst.expires) {
>  				/* Entry is expired even if it is in use */
>  				if (time_before_eq(jiffies, rth->u.dst.expires)) {
> -nofree:
>  					tmo >>= 1;
>  					rthp = &rth->u.dst.rt_next;
> -					/*
> -					 * We only count entries on
> -					 * a chain with equal hash inputs once
> -					 * so that entries for different QOS
> -					 * levels, and other non-hash input
> -					 * attributes don't unfairly skew
> -					 * the length computation
> -					 */
> -					for (aux = rt_hash_table[i].chain;;) {
> -						if (aux == rth) {
> -							length += ONE;
> -							break;
> -						}
> -						if (compare_hash_inputs(&aux->fl, &rth->fl))
> -							break;
> -						aux = aux->u.dst.rt_next;
> -					}
>  					continue;
>  				}
> -			} else if (!rt_may_expire(rth, tmo, ip_rt_gc_timeout))
> -				goto nofree;
> +			} else if (!rt_may_expire(rth, tmo, ip_rt_gc_timeout)) {
> +				tmo >>= 1;
> +				rthp = &rth->u.dst.rt_next;
> +				continue;
> +			}
>  
>  			/* Cleanup aged off entries. */
>  			*rthp = rth->u.dst.rt_next;
>  			rt_free(rth);
>  		}
>  		spin_unlock_bh(rt_hash_lock_addr(i));
> -		sum += length;
> -		sum2 += length*length;
> -	}
> -	if (samples) {
> -		unsigned long avg = sum / samples;
> -		unsigned long sd = int_sqrt(sum2 / samples - avg*avg);
> -		rt_chain_length_max = max_t(unsigned long,
> -					ip_rt_gc_elasticity,
> -					(avg + 4*sd) >> FRACT_BITS);
>  	}
> +	rt_chain_length_max = ip_rt_gc_elasticity;
>  	rover = i;
>  }
>  
>
>
>   

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