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From "dave selby" <dave6...@googlemail.com>
Subject Re: [users@httpd] apache 5 x load, 15 x CPU load - whats happening ?
Date Wed, 12 Nov 2008 07:43:34 GMT
2008/11/11 André Warnier <aw@ice-sa.com>:
> dave selby wrote:
> [...]
>>
>> OK ... I did not realize that there would be competition, the CPU load
>> is not 100% so I don't understand why apache and firefox would be
>> competing ?
>>
> It is a bit difficult to tell what is really happening, which is why it may
> be better trying to isolate the different aspects and really finding out who
> is using which resources for what.
>
> Now I'm really guessing, which is the best that can be done for now.
>
> You browser is getting a 28 Kbyte image from the server 5 times per second.
> The server has to get this data, which means disk I/O, which also means CPU
> time.
> The browser is probably doing something with that data, if only updating its
> cache maybe.  More disk I/O. So you may have one or the other process
> waiting for a chance to use the (same) disk, and spending CPU time on that.
>  If the browser is displaying the images, it needs memory to do so. There
> may be other processes involved too (I see at least two other processes
> which in your second "top", are also using considerably more CPU than in the
> first one). If the total memory needed by your browser, plus all the other
> apps including Apache, exceeds the physical memory available, there will be
> memory swapping going on.  That also costs CPU time, and extra I/O activity
> that itself needs more CPU time to handle it.
> And all these things, the way you are running them, are very inter-dependent
> and happen at the same time : it is precisely when your browser is having to
> work hardest to get the images, that your Apache also has to work harder, to
> deliver them.  Since you have a single CPU, it means that there will have to
> be many more context switches from your Apache process to your browser
> process, and so on.
> See what I mean ? No wonder you get an exponential behaviour.
>
> The type of Apache you are using may also be playing a role. It looks as if
> it is a threaded version, which maybe in this particular case also has a
> particularly adverse behaviour.

Many thanks for taking the time to explain this to me, I really
appreciate you taking the time to make this clear.

I will split the server / browser onto 2 x machines and post back the results

Thanks once again

Dave




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