From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dean Prichard To: Cc: <9fans@cse.psu.edu> Subject: Re: [9fans] netpipe results In-Reply-To: <28cad8ba36afb58990abc0895bf046e3@plan9.bell-labs.com> Message-ID: <20020312174234.K27487-100000@fbsd.acl.lanl.gov> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Date: Tue, 12 Mar 2002 18:00:27 -0700 Topicbox-Message-UUID: 657b1122-eaca-11e9-9e20-41e7f4b1d025 Andrey and I spend some time trying out different values of QMAX in /sys/src/9/ip/tcp.c. Increasing the size of QMAX seems to improve netpipe large packet behavior quite a bit. All tests were done using 2 800Mhz PIII machines with onboard i82557 ethernet. The graphs are available from http://www.acl.lanl.gov/plan9/netpipe/i82557.html The curves still flatten out above 32k data size, but it is much better than before once QMAX >= 256k. -dp On Sat, 9 Mar 2002 presotto@plan9.bell-labs.com wrote: > Date: Sat, 9 Mar 2002 08:52:00 -0500 > From: presotto@plan9.bell-labs.com > Reply-To: 9fans@cse.psu.edu > To: 9fans@cse.psu.edu > Subject: Re: [9fans] netpipe results > > Looks good. Is the 'data size' the size of a single write i.e. what the > NetPIPE paper calls 'block size'? If the latter, I can guess at some > explanations to start working at improving things. > > Looks like things start to fall off around 32K byte writes. Just looking > at numerology, that's what Maxatomic is set to in port/qio.c. It's > the point we start breaking writes into multiple blocks. I assume that > will have some affect though not a huge one. The drop we see at that > point is more than I would expect. The real nose dive happens > twixt 64k and 100k. 64k is the size of the per channel output queue. > After that, the system has to wait for the queue to half empty before > queuing any more. Just for a wild guess, it looks like we're getting > screwed by interaction twixt that histeresis and the process getting > rescheduled. There's similar problems with the size of the input > per channel queue (64k). Perhaps we should have spent more time > reading Kleinrock. > > These are just wild guesses. I'll start playing to see if I can explain > it, and preferably make it go away. I welcome anyone else doing the > same. > > Thanks much. It'll make a fun distraction. >