Re^3: system calls vs perl functions: Which should be faster in this example?

I have been working on something similar, so here are some tips that may improve your performance:

1. Improve the command execution time by using "lsof -Pn"

From the lsof manpage:
-P: This option inhibits the conversion of port numbers to port names for network files. Inhibiting the conversion may make lsof run a little faster.
-n: This option inhibits the conversion of network numbers to host names for network files. Inhibiting conversion may make lsof run faster. It is also useful when host name lookup is not working properly.

2. Reduce the overall output size and improve parsing by using "lsof -Pn -F" (The -F option is specifically intended for post-processing scripts like perl)

Although more complex, the same information is presented in a terse representation, for some perl examples have a look in the lsof "scripts" directory.

Here is the list_fields.pl example, which illustrates the parsing technique:

$fhdr = 0;# fd hdr. flag
$fdst = 0;# fd state
$access = $devch = $devn = $fd = $inode = $lock = $name = "";# | file 
+descr.
$offset = $proto = $size = $state = $stream = $type = "";# | variables
$pidst = 0;# process state
$cmd = $login = $pgrp = $pid = $ppid = $uid = "";# process var.

# Process the ``lsof -F'' output a line at a time, gathering
# the variables for a process together before printing them;
# then gathering the variables for each file descriptor
# together before printing them.

while (<>) {
    chop;
    if (/^p(.*)/) {

# A process set begins with a PID field whose ID character is `p'.

$tpid = $1;
if ($pidst) { &list_proc }
$pidst = 1;
$pid = $tpid;
if ($fdst) { &list_fd; $fdst = 0; }
next;
    }

# Save process-related values.

    if (/^g(.*)/) { $pgrp = $1; next; }
    if (/^c(.*)/) { $cmd = $1; next; }
    if (/^u(.*)/) { $uid = $1; next; }
    if (/^L(.*)/) { $login = $1; next; }
    if (/^R(.*)/) { $ppid = $1; next; }

# A file descriptor set begins with a file descriptor field whose ID
# character is `f'.

    if (/^f(.*)/) {
$tfd = $1;
if ($pidst) { &list_proc }
if ($fdst) { &list_fd }
$fd = $tfd;
$fdst = 1;
next;
    }

# Save file set information.

    if (/^a(.*)/) { $access = $1; next; }
    if (/^C(.*)/) { next; }
    if (/^d(.*)/) { $devch = $1; next; }
    if (/^D(.*)/) { $devn = $1; next; }
    if (/^F(.*)/) { next; }
    if (/^G(.*)/) { next; }
    if (/^i(.*)/) { $inode = $1; next; }
    if (/^k(.*)/) { next; }
    if (/^l(.*)/) { $lock = $1; next; }
    if (/^N(.*)/) { next; }
    if (/^o(.*)/) { $offset = $1; next; }
    if (/^P(.*)/) { $proto = $1; next; }
    if (/^s(.*)/) { $size = $1; next; }
    if (/^S(.*)/) { $stream = $1; next; }
    if (/^t(.*)/) { $type = $1; next; }
    if (/^T(.*)/) {
if ($state eq "") { $state = "(" . $1; }
else { $state = $state . " " . $1; }
next;
    }
    if (/^n(.*)/) { $name = $1; next; }
    print "ERROR: unrecognized: \"$_\"\n";
}

# Flush any stored file or process output.

if ($fdst) { &list_fd }
if ($pidst) { &list_proc }
exit(0);


## list_fd -- list file descriptor information
#      Values are stored inelegantly in global variables.

sub list_fd {
    if ( ! $fhdr) {

    # Print header once.

print "      FD   TYPE      DEVICE   SIZE/OFF      INODE  NAME\n";
$fhdr = 1;
    }
    printf "    %4s%1.1s%1.1s %4.4s", $fd, $access, $lock, $type;
    $tmp = $devn; if ($devch ne "") { $tmp = $devch }
    printf "  %10.10s", $tmp;
    $tmp = $size; if ($offset ne "") { $tmp = $offset }
    printf " %10.10s", $tmp;
    $tmp = $inode; if ($proto ne "") { $tmp = $proto }
    printf " %10.10s", $tmp;
    $tmp = $stream; if ($name ne "") { $tmp = $name }
    print "  ", $tmp;
    if ($state ne "") { printf " %s)\n", $state; } else { print "\n"; 
+}

# Clear variables.

    $access = $devch = $devn = $fd = $inode = $lock = $name = "";
    $offset = $proto = $size = $state = $stream = $type = "";
}


# list_proc -- list process information
#       Values are stored inelegantly in global variables.

sub list_proc {
    print "COMMAND       PID    PGRP    PPID  USER\n";
    $tmp = $uid; if ($login ne "") {$tmp = $login }
    printf "%-9.9s  %6d  %6d  %6d  %s\n", $cmd, $pid, $pgrp, $ppid, $t
+mp;

# Clear variables.

    $cmd = $login = $pgrp = $pid = $uid = "";
    $fhdr = $pidst = 0;
}
[download]

(The code was written by the lsof author, Victor A. Abell).

0xbeef

Comment on Re^3: system calls vs perl functions: Which should be faster in this example? Download Code

Replies are listed 'Best First'.

Re^4: system calls vs perl functions: Which should be faster in this example?
by machinecraig (Monk) on Dec 07, 2005 at 16:41 UTC

#!/usr/bin/perl -w
use Benchmark qw(:all);
use strict;

my $process = "processX";
my $lsofcmd1 = "/usr/local/bin/lsof -Pn -c $process|wc -l";
my $lsofcmd2 = "/usr/local/bin/lsof -c $process|wc -l";
my $count = 1000;

my $results = timethese($count,
        {
            'lsof_Pn_c' => sub { system($lsofcmd1);},
            'lsof_c' => sub { system($lsofcmd2); },
        },
        'none'
    );
print ("\n\n");
cmpthese( $results ) ;

### Results (ran it several times and got similar numbers) ###
#             Rate     lsof_Pn_c    lsof_c
# lsof_Pn_c   370/s           --       -0%
# lsof_c      372/s           0%        --
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