mirror of https://github.com/BOINC/boinc.git
81 lines
2.8 KiB
PHP
81 lines
2.8 KiB
PHP
|
<?php
|
||
|
|
require_once("docutil.php");
|
||
|
|
page_head("More about benchmarks");
|
||
|
|
echo "
|
||
|
|
<h2>How benchmarks are calculated</h2>
|
||
|
|
|
||
|
|
<p>
|
||
|
|
'Whetstone' is the name of the benchmark that is reported on your
|
||
|
|
[Show computers] web page as 'Measured floating point speed'.
|
||
|
|
Dhrystone is the name of the benchmark used for 'Measured integer speed'.
|
||
|
|
Floats can have fractional parts (like 1.48283 or 3.141592);
|
||
|
|
integers are whole numbers like 1, 2, 938283 or 2004.
|
||
|
|
|
||
|
|
Whetstone does 8 different groups of tests (repeatedly of course),
|
||
|
|
times how long they took to finish, and produces a number,
|
||
|
|
[ops performed]/[time].
|
||
|
|
These tests all use floating point math operations of the CPUs being tested.
|
||
|
|
Some of them are simple math (addition, multiplication, division)
|
||
|
|
while others compute trigonometric and exponential functions
|
||
|
|
(sine, cosine, tangent, exponent).
|
||
|
|
|
||
|
|
|
||
|
|
Dhrystone checks repeated integer operations
|
||
|
|
and several operating system file handling operations.
|
||
|
|
|
||
|
|
<p>
|
||
|
|
Neither of the tests really checks how well/fast a system can access memory,
|
||
|
|
and SETI@home (for example) accesses memory a lot.
|
||
|
|
|
||
|
|
<p>
|
||
|
|
Here is an example of memory introducing a delay:
|
||
|
|
A Pentium 4 CPU of any speed can calculate the sine of an angle in
|
||
|
|
approximately 170 ticks of its internal clock.
|
||
|
|
It could have performed 170 regular integer additions in this time.
|
||
|
|
|
||
|
|
<p>
|
||
|
|
But if it wanted to do an integer addition on a number somewhere out in memory
|
||
|
|
(say it was working on a table of numbers), the
|
||
|
|
CPU might have to wait as much as 260 ticks
|
||
|
|
for this memory integer to be delivered to the CPU.
|
||
|
|
So a badly timed integer+memory
|
||
|
|
operation would take far longer than a sine calculation.
|
||
|
|
|
||
|
|
<p>
|
||
|
|
This is where Celeron CPUs can really slow down.
|
||
|
|
Pentium has many features to predict when the CPU might be getting memory,
|
||
|
|
and begins getting it long before the CPU actually calculates with it.
|
||
|
|
Thus there is much less delay for most memory operations.
|
||
|
|
|
||
|
|
<h2>Why 'predicted time' can be wrong</h2>
|
||
|
|
Each WU delivered to your machine includes an estimated number of
|
||
|
|
floating point (FP) calculations.
|
||
|
|
BOINC divides this by the FP
|
||
|
|
benchmark number to estimate completion time.
|
||
|
|
SETI@home's WUs estimate number is currently always 27.9 trillion (american),
|
||
|
|
however the actual number of FP ops varies greatly which is why
|
||
|
|
WUs take different amounts of time to finish.
|
||
|
|
|
||
|
|
|
||
|
|
<p>
|
||
|
|
SETI@home uses almost all single-precision floating point math,
|
||
|
|
while Whetstone is all double-precision math.
|
||
|
|
On Intel x86 processors
|
||
|
|
the speed difference in calculating single vs. double isn't very large.
|
||
|
|
|
||
|
|
<p>
|
||
|
|
SETI@home uses mostly add, sub, multiply and divide.
|
||
|
|
About 20% of its time is spent in trigonometry.
|
||
|
|
Almost all the time in Whetstone is used for trigonometry.
|
||
|
|
|
||
|
|
<p>
|
||
|
|
Memory access speed and trigonometry are the two major reasons that
|
||
|
|
the benchmark results and SETI@home processing speed don't match
|
||
|
|
up on many systems.
|
||
|
|
|
||
|
|
<br><br>
|
||
|
|
<i>Thanks to Ben Herndon for this writeup</i>
|
||
|
|
";
|
||
|
|
page_tail();
|
||
|
|
?>
|