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Thread: CPU usage

  1. #1
    SitePoint Evangelist
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    CPU usage

    I'm sorry if this is slightly off-topic...

    In a post elsewhere I'd asked: If a shared host is offering 'CPU limit - 100% of CPU for 8 seconds maximum' - does that mean that if one site has a poorly-written script or some other resource-hogging activity, that the server wouldn't be able to serve pages and process requests from others during that time?

    I'm wondering just what might actually tie-up a cpu for so long.

    (Personally, I've been on a dedicated server for some time - since I encountred the issue of Movable Type installs timing-out during rebuilds.)

  2. #2
    SitePoint Wizard silver trophy Karl's Avatar
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    Hi,

    I've actually just answered that in your other thread Basically no it doesn't as the OS scheduler will allow other processes to run as well, and the host in question most likely means 100% of 1 CPU Core as well.

    Thanks,
    Karl Austin :: Profile :: KDA Web Services Ltd.
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    Thanks.

    So does an OS Scheduler 'interupt' processes at tiny intervals... so's to prevent one process from having the whole cpu - and thus make multiple processes run 'simultaneously' (even though they're each being temporarily halted for a few milliseconds to allow something else to be processed?

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    SitePoint Wizard silver trophy Karl's Avatar
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    Hi,

    Yes, that's pretty much how modern day multi-tasking works, obviously now systems with multiple CPUs are common so you do genuinely get 2 or more processes r inning at exactly the same time as well. The other main hinge is interrupts from devices, that interrupt the CPU to let them know they have work that needs doing I.e. Network cards etc.

    Thanks,
    Karl Austin :: Profile :: KDA Web Services Ltd.
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    Call 0800 542 9764 today and ask how we can help your business grow.

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    Excellent, thanks karl - appreciated.

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    SitePoint Wizard silver trophy ldcdc's Avatar
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    If a shared host is offering 'CPU limit - 100% of CPU for 8 seconds maximum'
    In any case, you must take such policies with a grain of salt, when talking about shared hosting environments. If you're guaranteed that, and 200 other customers are guaranteed the same, should 10 of you need 10% of CPU for and indefinite period of time, and 2 other customer require their 100% from time to time, will they let that go on indefinitely? The answer is very unlikely to be "yes".
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    Thanks. I wasn't looking to utilise such availability, rather to clarify something and confim my view of just how unsuitable shared hosting really can be... especially if a site is able to have 100% cpu for as long as stated - which, with my limited knowledge, seemed totally unacceptable.

    But, now understanding things a little more, it's clearly not as bad as I thought as the cpu can't be fully occupied for so long by a single site.


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