Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris
 
PerlMonks  

Re: does perl have branch prediction

by oiskuu (Friar)
on Jan 29, 2014 at 12:24 UTC ( #1072499=note: print w/ replies, xml ) Need Help??


in reply to does perl have branch prediction

Note that CPUs (these days) support conditional instructions; good compilers make use of these. Loop body such as

if (v[i] >= 128) sum += v[i];
is likely compiled with a cmov on x86/x86_64 and therefore incurs no branch misprediction penalty.

As for the perl version: the effects of misprediction are practically negligible, lost in the noise.

perf stat perl5.18.1 -e '@a = map {($i += 1.1e-0) + rand} 1..3e6; $i = + $i/2 + 0.5; $_ > $i and $n+=$_ for @a;' 8509781489 instructions 1701278883 branches 3938702 branch-misses 1.561091272 seconds time elapsed perf stat perl5.18.1 -e '@a = map {($i += 1.1e-10) + rand} 1..3e6; $i += $i/2 + 0.5; $_ > $i and $n+=$_ for @a;' 8505802267 instructions 1700634854 branches 5437641 branch-misses 1.567880931 seconds time elapsed


Comment on Re: does perl have branch prediction
Select or Download Code

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1072499]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others about the Monastery: (7)
As of 2015-07-31 05:26 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









    Results (274 votes), past polls