Re: [OT] Mail hangs real-time processes
Re: [OT] Mail hangs real-time processes
- Subject: Re: [OT] Mail hangs real-time processes
- From: Herbie Robinson <email@hidden>
- Date: Thu, 8 Jan 2004 16:50:26 -0500
At 10:22 AM -0800 1/7/04, Jeff Moore wrote:
If you take a page fault in any thread, the thread that services it
in the kernel is higher priority than any real time thread. What you
can end up with is a kind of priority inversion where some normal
priority thread is causing work to be done on a very high priority
thread.
One possible explanation of this situation is that opening such a
large mail box is thrashing the heck out of the VM system which
would prevent the HAL's IO thread in iTunes from running.
That sounds like the wrong thing for the OS to be doing. The
real-time threads should have higher priority than page fault
handling. Still, it's not as bad as I thought at first. The real
time threads still have higher priority than the threads that are
actually causing the page faults; so, once the real time threads get
scheduled, the page fault rate will be cut down or even stop. In
fact, on a single CPU system, the only effect will be to delay
scheduling a real time thread for the amount of time it takes to
queue disk I/O for one page fault (which is probably not much time).
Actually, I think that the same is true for multiple CPUs with
multiple real-time threads.
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