On 5/23/06, Wiggins, Mark <[EMAIL PROTECTED]> wrote:
1) If the timer patch has been off for all of this time, is it worth turning on now?
The point of the hz_timer is to get periods of inactivity long enough that CP can conclude that the server is apparently idle and review the use of real memory of that server. If the timer interrupts keep the server in queue all the time you eventually end up in Q3 even though your CPU usage is minimal. The amount of work that Linux does on each timer tick is minimal, so the reduction in CPU usage may not be that exciting. My server drops from 0.20% to 0.08%, but that really depends on what your idle server has still going on. With hz_timer=0 the only timer interrupts are when a process asks for the wake-up call. There are some applications that schedule a lot of wake-up calls. I know some applications schedule a wake-up every 25mS - that's about as bad as polling with 10mS, and it certainly does not give CP the 300 mS it needs for queue drop. z/VM 5.2 has some new function to review memory usage of an idle server, even when it does not drop from queue. I have not seen any numbers from that yet, so I cannot tell how effective it is.
3) Are there any particular instances where you wouldn't turn the patch on? E.g. a time server or maybe a mail server??? I don't know... Only test servers??? Etc...
The previous incarnation of the timer patch was more expensive on a busy server (because the number of timer interrupts ended up being way more than once every 10mS). With the current implementation this is not an issue anymore. If anyone has measured the hz_timer=1 being a performance improvement, I would be interested to see their numbers. I have not seen it yet. Maybe part of this is due to the belief that if it burns more gas it must be faster... Rob -- Rob van der Heij Velocity Software, Inc http://velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
