PHP-FPM [download server] - php file run very slow

Hi, first sorry for my english skill.

I have problem. I build server for download file. Few week ago, all thing was ok. But now download file very slow processing, some time error (long time run php file).
I try reboot server, download file is back to normal, but few hour later download file slow again.

here my top command result:


all is ok, load average or % wa speed.

try download file in direct link is ok (ex: http://myserv.com/data/file.zip)

but download via php script is very slow (some time error)

ex: http://myserv.com/download.php?file=abc

---

here is my download.php method:

PHP:

<?php
$file = '/path/to/files/photo.jpg';
if (is_file($file))
{
    sendHeaders($file, 'image/jpeg', 'My picture.jpg');
    $chunkSize = 1024 * 1024;
    $handle = fopen($file, 'rb');
    while (!feof($handle))
    {
        $buffer = fread($handle, $chunkSize);
        echo $buffer;
        ob_flush();
        flush();
    }
    fclose($handle);
    exit;
}
?>

ah, when in "slow" time, try some php with only echo text function still slow too,
mean link http://myserv.com/echo.php will run very slow too.

So is there any wrong was there.
I checked server running ok, no any program make overload cpu, or long time. but download via php file very slow.

can help me this big problem.

thank very much

 

thank very much, I will try in your way.

thanks again