Re: [PATCH - RFC] [1/5] 64-bit network statistics - generic net

[Jeff Sipek <jeffpc@optonline.net>]

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On Thursday 03 July 2003 23:08, Linus Torvalds wrote:
> Please do this in user space. The "overflow every 2^32 packets" thing is
> _not_ a problem, if you just gather the statistics at any kind of
> reasonable interval.

The packet counters are fine (for now, that is), but the tx_bytes and rx_bytes 
counters need those 64-bits. 4GB (= 2^32 bytes) is not enough. For example:

- - gigabit ethernet will cause 32-bit counters to overflow about every 34 
seconds (at full speed.)
- - 10Gb/s ethernet will only take about 3.4 seconds
- - a user like me, who has 5Mbit/s connection to the net can cause the counter 
to overflow in 1 hour 54 minutes

(Most of the time, the devices are not maxed out, but we have to check the 
worst case scenario.) Now, how often should the user space 
statistics-gathering program should run? Well, at least every 30 seconds, for 
now that should be good, but the rein of 10Gb/s is approaching...

> I'd hate to penalise performance for something like this. We have
> generally avoided locking _entirely_ for statistics, exactly because
> people felt that there are major performance issues wrt network packet
> handling, and that "perfect statistics" aren't important enough to
> penalize performance over.

I agree with you, that is why I made it optional so the user may choose to 
sacrifice performace for statistics when needed.

Additionally, I am sure there is a way of optimizing the patch I wrote (i.e. 
actual transmition is locked with a lock from struct net_device.) I am aware 
that this patch is a major undertaking, but it is only a matter of time 
before someone will have to do it anyway.

> Remember: "perfect is the enemy of good".

Very true.


Jeff.

- -- 
Only two things are infinite, the universe and human stupidity, and I'm 
not sure about the former.
		- Albert Einstein
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