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

[Nicolas Cellier]

2011/1/11 Eliot Miranda <eliot.miranda at gmail.com>:
>
>
>
> On Tue, Jan 11, 2011 at 12:26 PM, Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com> wrote:
>>
>> 2011/1/11 Eliot Miranda <eliot.miranda at gmail.com>:
>> >
>> >
>> >
>> > 2011/1/11 Levente Uzonyi <leves at elte.hu>
>> >>
>> >>
>> >> On Tue, 11 Jan 2011, Eliot Miranda wrote:
>> >>
>> >> (Pine can't quote your mail, sorry.)
>> >>
>> >> "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."
>> >>
>> >> What about keeping the priority of the heartbeat thread at user-level and decreasing the other VM threads' priority slighly?
>> >
>> > 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...
>
> You don't have to confirm this.  We have confirmed this at length over the past year at Teleplace.  realtime scheduling is /not allowed/ in non-super-user processes.  So unless the Squeak VM is to be installed setuid and run as root it, like all other non-setuid programs on linux, must make do with a /single/ thread priority.
> I have a _few_ test programs that you're welcome to try out if you really don't believe me :)
> best
> Eliot

Hmm yes, i was just browsing
man 7 capabilities
very defensive...

Nicolas

>>
>> Nicolas
>>
>> >>
>> >> Levente
>> >
>> >
>> >
>
>
>