[Vm-dev] Re: [Pharo-project] Waste of CPU Power by polling events?

[Nicolas Cellier]

2011/1/11 Eliot Miranda <eliot.miranda at gmail.com>:
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> 2011/1/11 Levente Uzonyi <leves at elte.hu>
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>> On Tue, 11 Jan 2011, Eliot Miranda wrote:
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>> (Pine can't quote your mail, sorry.)
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>> "The problem with linux is that the pthreads implementation doesn't allow a normal user-level process to create high-priroity threads so that as
>> soon as the Vm starts to spin doing some computation the heartbeat thread is shut-out and if the spinning computation only interrupted when a delay
>> expires it'll never get interrupted because it is blocking the very thread that would signal the delay.  So until linux's pthreads implementation
>> supports multiple priorities we're stuck with hacks like the interval timer based itimer in the linux Cog VMs."
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>> What about keeping the priority of the heartbeat thread at user-level and decreasing the other VM threads' priority slighly?
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> Linux doesn't allow more than /one/ thread priority for threads in a user-level process.   So one /can't/ have multiple priorities.  All threads run at the same priority.  This is a horrible bug in the linux pthreads implementation but there it is.
> best
> Eliot

Superficial googling "setting linux pthread priority" gives me this
thread (java)
http://kerneltrap.org/node/6080

It seems that there are different scheduling policies in linux 2.6
kernel, realTime, and non real time (traditional unix time sharing).
It seems that only real time threads can have their priority set.

man sched_setscheduler

After man 7 pthreads, it appears that the scheduling policy would be
different for each thread.

However, the functionalities of interest are provided by the NPTL
(Native POSIX Threads Library).
The older LinuxThreads implementation might not implement POSIX.1
complying threads.

So, some linux might work, for example, in my fresh mandriva 2010.2
x86-32, I test
$ getconf GNU_LIBPTHREAD_VERSION
NPTL 2.11.1

To be confirmed...

Nicolas

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>> Levente
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