netdev - Re: questions on NAPI processing latency and dropped network packets

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Message-ID: <478CCC95.8030405@hp.com>
Date:	Tue, 15 Jan 2008 10:09:09 -0500
From:	Vlad Yasevich <vladislav.yasevich@...com>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	Eric Dumazet <dada1@...mosbay.com>, Ray Lee <ray-lk@...rabbit.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: questions on NAPI processing latency and dropped network packets

Chris Friesen wrote:
> Eric Dumazet wrote:
>> Chris Friesen a écrit :
> 
>>> Based on the profiling information we're spending time in 
>>> sctp_endpoint_lookup_assoc() which doesn't actually use hashes, so I 
>>> can't see how the hash would be related.  I'm pretty new to SCTP 
>>> though, so I may be missing something.
>>
>> Well, it does use hashes :)
>>
>>        hash = sctp_assoc_hashfn(ep->base.bind_addr.port, rport);
>>        head = &sctp_assoc_hashtable[hash];
>>        read_lock(&head->lock);
>>        sctp_for_each_hentry(epb, node, &head->chain) {
>>            /* maybe your machine is traversing here a *really* long 
>> chain */
>>            }
> 
> 
> The latest released kernel doesn't have this code, it was only added in 
> November.  The SCTP maintainer just pointed me to the patch, and made 
> some other suggestions as well.
> 

Yes,  the hash code only got added to 2.6.24.  Before that, it was
a linear list traversal which sucked.

I need to take a look at the locking to see if we can further reduce
the time that bottom half is disabled.

-vlad
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