linux-kernel - Re: 2048 CPUs [was: Re: New filesystem for Linux]

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Message-ID: <20061110090303.GB3196@elf.ucw.cz>
Date:	Fri, 10 Nov 2006 10:03:03 +0100
From:	Pavel Machek <pavel@....cz>
To:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:	Albert Cahalan <acahalan@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: 2048 CPUs [was: Re: New filesystem for Linux]

Hi!

> >>If some rogue threads (and it may not even be intetional) call the same
> >>syscall stressing the one spinlock all the time, other syscalls needing
> >>the same spinlock may stall.
> >
> >Fortunately, they'll unstall with probability of 1... so no, I do not
> >think this is real problem.
> 
> You can't tell that CPUs behave exactly probabilistically --- it may 
> happen that one gets out of the wait loop always too late.

Well,  I don't need them to be _exactly_ probabilistical.

Anyway, if you have 2048 CPUs... you can perhaps get some non-broken
ones.

> >If someone takes semaphore in syscall (we do), same problem may
> >happen, right...? Without need for 2048 cpus. Maybe semaphores/mutexes
> >are fair (or mostly fair) these days, but rwlocks may not be or
> >something.
> 
> Scheduler increases priority of sleeping process, so starving process 
> should be waken up first. But if there are so many processes, that
>process

I do not think this is how Linux scheduler works.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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