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diff --git a/share/doc/papers/diskperf/methodology.ms b/share/doc/papers/diskperf/methodology.ms new file mode 100644 index 000000000000..703d7b6f0545 --- /dev/null +++ b/share/doc/papers/diskperf/methodology.ms @@ -0,0 +1,111 @@ +.\" Copyright (c) 1983 The Regents of the University of California. +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)methodology.ms 6.2 (Berkeley) 4/16/91 +.\" +.ds RH Methodology +.NH +Methodology +.PP +Our goal was to evaluate the performance of the target peripherals +in an environment as much like our 4.2BSD UNIX systems as possible. +There are two basic approaches to creating this kind of test environment. +These might be termed the \fIindirect\fR and the \fIdirect\fR approach. +The approach used by DEC in producing most of the performance data +on the UDA50/RA81 system under VMS is what we term the indirect +approach. +We chose to use the direct approach. +.PP +The indirect approach used by DEC involves two steps. +First, the environment in which performance is to be evaluated +is parameterized. +In this case, the disk I/O characteristics of VMS were measured +as to the distribution of various sizes of accesses and the proportion +of reads and writes. +This parameterization of +typical +I/O activity was termed a +``vax mix.'' +The second stage involves simulating this mixture of I/O activities +with the devices to be tested and noting the total volume of transactions +processed per unit time by each system. +.PP +The problems encountered with this indirect approach often +have to do with the completeness and correctness of the parameterization +of the context environment. +For example, the +``vax mix'' +model constructed for DECs tests uses a random distribution of seeks +to the blocks read or written. +It is not likely that any real system produces a distribution +of disk transfer locations which is truly random and does not +exhibit strong locality characteristics. +.PP +The methodology chosen by us is direct +in the sense that it uses the standard structured file system mechanism present +in the 4.2BSD UNIX operating system to create the sequence of locations +and sizes of reads and writes to the benchmarked equipment. +We simply create, write, and read +files as they would be by user's activities. +The disk space allocation and disk cacheing mechanism built into +UNIX is used to produce the actual device reads and writes as well +as to determine their size and location on the disk. +We measure and compare the rate at which these +.I +user files +.R +can be written, rewritten, or read. +.PP +The advantage of this approach is the implicit accuracy in +testing in the same environment in which the peripheral +will be used. +Although this system does not account for the I/O produced +by some paging and swapping, in our memory rich environment +these activities account for a relatively small portion +of the total disk activity. +.PP +A more significant disadvantage to the direct approach +is the occasional difficulty we have in accounting for our +measured results. +The apparently straight-forward activity of reading or writing a logical file +on disk can produce a complex mixture of disk traffic. +File I/O is supported by a file management system that +buffers disk traffic through an internal cache, +which allows writes to ba handled asynchronously. +Reads must be done synchronously, +however this restriction is moderated by the use of read-ahead. +Small changes in the performance of the disk controller +subsystem can result in large and unexpected +changes in the file system performance, +as it may change the characteristics of the memory contention +experienced by the processor. +.ds RH Tests +.bp |