Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!cunixf.cc.columbia.edu!cs.columbia.edu!bill From: bill@cs.columbia.edu (Bill Schilit) Newsgroups: comp.os.mach Subject: Re: Mach RPC Throughput... Message-ID: Date: 15 Mar 91 05:52:54 GMT References: Sender: bill@cs.columbia.edu (Bill Schilit) Distribution: comp Organization: Columbia University Department of Computer Science Lines: 35 In-Reply-To: morse@quark.mpr.ca's message of 14 Mar 91 14:16:59 GMT Our measurements of Mach RPC show that TCP is the dominant cost when sending synchronous RPC consisting of a small request and a 4K response. On an i386 machine with an AT bus running Mach 2.5 we tried to account for the measured round trip time of 33ms by computing the cost of ethernet and bus transfer and separately measuring TCP loopback and Mach RPC without going over the network. The results are shown below. 4K RPC ------ Packets 7 (observed) Bytes 4738 (observed) AT bus (times 2) 9.5 ms (computed) Ethernet 3.8 ms (computed) TCP Loopback 12 ms (measured) Mach IPC (times 2) 4 ms (measured) Total 29.3 ms Network RPC 33 ms (measured) Breaking the times down with into these four components gets pretty close to the observed network RPC rate. These tests are fully described in "Adaptive remote paging for mobile computing" TR CUCS-004-91, available by anonymous FTP from cs.columbia.edu::pub/reports. - Bill -- Bill Schilit Columbia University Computer Science Department bill@cs.columbia.edu