Basic Costs in MILLIPAGE

A major goal in MILLIPAGE's design was to minimize the DSM protocol time by implementing a thin protocol layer. Table 1 shows the measured times (costs) of some basic operations that are part of the DSM protocols in MILLIPAGE.

 

Table 1: Cost of basic operations in MILLIPAGE.

operation	$\mu{}s$
access fault	26
get protection	7
set protection	12
header message send/recv (32 bytes)	12
a data message send/recv (0.5 KB)	22
a data message send/recv (1 KB)	34
a data message send/recv (4 KB)	90
minipage translation (MPT lookup)	7

 

The time it takes to bring in a page for reading in MILLIPAGE is 204 $\mu{}s$ for minipages of size 128 byte, and 314 $\mu{}s$ for minipages of size 4 KB. The difference in arrival times for a minipage request arriving in a single hop as opposed to two hops was slight. The time it takes to bring in a page for writing in MILLIPAGE is 212-366 $\mu{}s$ for 128 bytes minipages, and 327-480 $\mu{}s$ for 4KB minipages. These times vary according to the number of read copies that should be invalidated prior to serving the write request.

A barrier between 1 to 8 hosts takes 59-153 $\mu{}s$ (linearly in the number of hosts) and a lock followed by an unlock operation takes 67-80 usec.

In addition, we measured diff creation time in our setting. Our measurements show that a run-length diff operation (as described in [5]) for 4KB page takes 250 $\mu{}s$ and decreases linearly with the size of the page. Obviously, this time is not negligible, and would have dominated the overhead if it were required in the DSM protocol.