GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages


Manual Reference Pages  -  BW_MEM (8)

NAME

bw_mem - time memory bandwidth

CONTENTS

Synopsis
Description
Output
Memory Utilization

SYNOPSIS

bw_mem_cp [ -P <parallelism> ] [ -W <warmups> ] [ -N <repetitions> ] size rd|wr|rdwr|cp|fwr|frd|bzero|bcopy [align]

DESCRIPTION

bw_mem allocates twice the specified amount of memory, zeros it, and then times the copying of the first half to the second half. Results are reported in megabytes moved per second.

The size specification may end with ‘‘k’’ or ‘‘m’’ to mean kilobytes (* 1024) or megabytes (* 1024 * 1024).

OUTPUT

Output format is "%0.2f %.2f\n", megabytes, megabytes_per_second, i.e.,

8.00 25.33

There are nine different memory benchmarks in bw_mem. They each measure slightly different methods for reading, writing or copying data.
rd measures the time to read data into the processor. It computes the sum of an array of integer values. It accesses every fourth word.
wr measures the time to write data to memory. It assigns a constant value to each memory of an array of integer values. It accesses every fourth word.
rdwr measures the time to read data into memory and then write data to the same memory location. For each element in an array it adds the current value to a running sum before assigning a new (constant) value to the element. It accesses every fourth word.
cp measures the time to copy data from one location to another. It does an array copy: dest[i] = source[i]. It accesses every fourth word.
frd measures the time to read data into the processor. It computes the sum of an array of integer values.
fwr measures the time to write data to memory. It assigns a constant value to each memory of an array of integer values.
fcp measures the time to copy data from one location to another. It does an array copy: dest[i] = source[i].
bzero measures how fast the system can bzero memory.
bcopy measures how fast the system can bcopy data.

MEMORY UTILIZATION

This benchmark can move up to three times the requested memory. Bcopy will use 2-3 times as much memory bandwidth: there is one read from the source and a write to the destionation. The write usually results in a cache line read and then a write back of the cache line at some later point. Memory utilization might be reduced by 1/3 if the processor architecture implemented ‘‘load cache line’’ and ‘‘store cache line’’ instructions (as well as ‘‘getcachelinesize’’).

SEE ALSO

lmbench(8).

AUTHOR

Carl Staelin and Larry McVoy

Comments, suggestions, and bug reports are always welcome.

Search for    or go to Top of page |  Section 8 |  Main Index


(c)1994-2000 Larry McVoy and Carl Staelin BW_MEM (8) $Date$

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.