Re: [Chromium-dev] More fun with the network layers

[Mike H. <mho...@gr...>]

Karl Rasche wrote:

>>>>The bad news.  Take a look at NetRecv...  We check all of the layers one 
>>>>by one.  I've fixed things in my version so that we only check a layer 
>>>>if we actually have connections of that type instead of always checking 
>>>>layers like TCPIP and FILE.  However, if we have a TCPIP connection 
>>>>active, we will call TCPIPRecv.  The problem is that if we don't send 
>>>>data on each tcpip connection (it loops through them all), we sit and 
>>>>wait for the select and transmit timeouts. 
>>>>   
>>>>
>>>>        
>>>>
>>>Is the problem that, no matter what, once some data comes in over tcpip, 
>>>we'll sit in tcpip_read_exact() until all the data has come in? Meanwhile, 
>>>everyone elses' data is ignored until tcpip is happy? I think i've hit 
>>>things like this before, but with fighting between tcpip connections, not 
>>>tcpip vs IB.
>>> 
>>>
>>>      
>>>
>>The issue I'm running into seems to be similar.  In the case of 
>>sort-last remote rendering, I want to use a highspeed network for 
>>compositing and then use tcpip to deliver the final images.  So, for 
>>each frame, there is going to be highspeed traffic(IB) for the 
>>composite, followed by slow traffic (GigE/100TX) for sending Chromium 
>>commands on the wire and displaying the final image.  However, since we 
>>check tcpip connections first, I hit the tcpip layer and then sit and 
>>wait for data to be sent. 
>>    
>>
>
>Ok, I'll try again :)
>
>So, the problem is waiting for select() to timeout because there isn't any 
>tcpip goodness coming over the wire yet?
>
>  
>
Yes.  I'll try mucking with the timeout to see if I can get performance 
back up.  I'll also look into what it's going to take to make the 
network layer not loop through every possible connection...

>  
>
>>IB stuff zips along followed by actual tcpip traffic.  This drops 
>>performance achievable over IB from ~700MB/s to about 30MB/s (OUCH!!!).
>>    
>>
>
>Hmm. one solution would be to trade me some IB for some 100mbps ethernet 
>;)
>
I wish things were cheap enough to lend to people.  ;-)

Actually, any highspeed layer is going to be hosed by this.  I thought 
you guys have a Myrinet cluster there?

-Mike