You should always show a complete, working example, so we don't have to guess or flesh out your script to test. From your complaint that the textview refresh is slow(fragmented), you probably need to force an update

$buffer->set_text($sysbuffer);
Gtk2->main_iteration while Gtk2->events_pending;
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is an often used code line that forces the gtk2 event loop to do one loop, and update everything.

Here is a pretty good complete scrolled textview example to help you out. (A commented out IO::Pipe method works too)

#!/usr/bin/perl -w
use strict;
use Glib  qw(TRUE FALSE);
use Gtk2 -init;
use Gtk2::Helper;

#use IO::Pipe;
#open a pipe to a command
#my $fh = new IO::Pipe;
#$fh->reader("top -b");
#$fh->reader("counter1.pl");

#open(FH, "counter1.pl |") or die "$!\n";
open(FH, "top -b |") or die "$!\n";

#add a watch to this file handle
my $helper_tag = Gtk2::Helper->add_watch(fileno FH, 'in',sub{
            &watch_callback('FH');
        });

#standard window creation, placement, and signal connecting
my $window = Gtk2::Window->new('toplevel');
$window->signal_connect('delete_event' => sub { exit;});
$window->set_border_width(5);
$window->set_position('center_always');

my $hbox = Gtk2::HBox->new();
$hbox->set( "border_width" => 0 );
$window->add($hbox);

my $scroll   = Gtk2::ScrolledWindow->new;
$scroll->set_size_request(600,600);
my $textview = Gtk2::TextView->new;
my $buffer = $textview->get_buffer;
create_tags($buffer);

$scroll->add($textview);
$hbox->pack_start($scroll,1, 1, 1 ); # expand?, fill?, padding;

$window->show_all();

#our main event-loop
Gtk2->main;

sub watch_callback {

    my ($fh) = @_;
    
    my $line;
    #read 1000 caracters of the buffer
    #$fh->sysread($line,1000);
    sysread(FH,$line,1000);
      
    #remove the newline
#    print $line;
    chomp $line;
    
    if($line){
           $buffer->insert_with_tags_by_name($buffer->get_end_iter, $l
+ine,'blue');
    }else{
           Gtk2::Helper->remove_watch($helper_tag);                 
    }

        
    #absolutely need the main iteration here, or you
    #won't get the end iter correctly 
        Gtk2->main_iteration while Gtk2->events_pending;
        $textview->scroll_to_iter($buffer->get_end_iter,0,0,0,0);

#        my $end_mark = $buffer->create_mark( 'end', $buffer->get_end_
+iter, FALSE );
#        $textview->scroll_to_mark( $end_mark, 0.0, FALSE, 0.0, 1.0 );


    #important so we can loop again    
    return 1;
}
###########################################3
sub create_tags{
  my $buffer = shift; 

   $buffer->create_tag('blue',
           foreground => 'blue',
           );

   $buffer->create_tag('col',
           foreground => 'green',
       );

}
#########################################
__END__
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