netdev - Re: [PATCH 7/7][TAKE 2][TFRC] New rx history code

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Message-ID: <20071205094237.GB5177@gerrit.erg.abdn.ac.uk>
Date:	Wed, 5 Dec 2007 09:42:37 +0000
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>, netdev@...r.kernel.org,
	dccp@...r.kernel.org
Subject: Re: [PATCH 7/7][TAKE 2][TFRC] New rx history code

| I found a problem that I'm still investigating if was introduced by this
| patch or if was already present. When sending 1 million 256 byte packets
| with ttcp over loopback, using ccid3 it is crashing, the test machine
| I'm using doesn't have a serial port, its a notebook, will switch to
| another that has and provide the backtrace. It doesn't happens every
| time.
| 
CCID3 is difficult due to the TX queue. Small packets are faster on the
wire, fill up the TX queue faster. Since there is little loss on LANs, 
the slow-start algorithm will soon reach link capacity; but CCID3 can
not deal effectively with high speeds.
What is known not to work well at the moment is bidirectional data
transfer (e.g. an echo server/client). This lead to the comment in
tfrc_rx_sample_rtt(); the support for bidirectional data transfer
needs some more work, which however requires to make one-directional
transfer work well first.

| Here is tfrc_rx_hist_alloc back using ring of pointers with the fixed
| error path.
| 
Thank you - I was just about to send a similar patch as update since
you clearly identified this bug. I will resubmit with your version
and upload it to the test tree.

| +int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)
|  {
| +	int i;
| +
| +	for (i = 0; i <= TFRC_NDUPACK; i++) {
| +		h->ring[i] = kmem_cache_alloc(tfrc_rx_hist_slab, GFP_ATOMIC);
| +		if (h->ring[i] == NULL)
| +			goto out_free;
| +	}
| +
| +	h->loss_count = h->loss_start = 0;
| +	return 0;
| +
| +out_free:
| +	while (i-- != 0) {
| +		kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
| +		h->ring[i] = NULL;
|  	}
| +	return -ENOBUFS;
|  }
| 
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