From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steve Modica Subject: Re: variation in thruput w/ change in mtu on gige Date: Mon, 26 Apr 2004 10:02:07 -0500 Sender: netdev-bounce@oss.sgi.com Message-ID: <408D246F.8090404@sgi.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@oss.sgi.com Return-path: To: Abhijit Karmarkar In-Reply-To: Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Probably page size. 4k is one page so those are probably the most efficient IOs. There must be some additional handling required to squeeze multiple pages into an MTU. Have you profiled things at all to see what additional code has to run in order to handle multiple pages? Steve Abhijit Karmarkar wrote: > Hi, > > i have observed that using jumbo frames (mtu=9000) decreases the thruput > (i am timing one-way ttcp). trying w/ different mtu's i see 4096 give > me the best numbers: > > mtu thruput > ------------------------------- > 1500 (default) ~846Mbps > 4096 ~930Mbps <== highest > 8192 ~806Mbps > 9000 ~806Mbps > 15K ~680Mbps > > my setup is: > - 2 nodes connected directly (cross-over cable) > - each node: 2-way, 2.4G Xeon. 4G RAM., running RHEL3 (2.4.21-4.ELsmp) > - intel gige (82543GC), e1000 ver. (5.1.11-k1) > i think the cards are: 64bit/66Mhz PCI. > - ipv4.tcp_r/wmem and core.r/wmem_max set sufficiently high (512KB) > - using ttcp to xfer ~8GB one-way. > > why doesn't my thruput increase with increase in MTU? is it because of > small number of rx/txdescriptors on 82543GC (max=256?) or something > else? > > are there any driver parameters that i can tune to get better numbers > with larger MTUs? > > thanks, > abhijit > -- Steve Modica work: 651-683-3224 MTS-Technical Lead "Give a man a fish, and he will eat for a day, hit him with a fish and he leaves you alone" - me