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

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Message-ID: <20061107212614.GA6730@ucw.cz>
Date:	Tue, 7 Nov 2006 21:26:14 +0000
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!

> >The SGI Altix can have 2048 CPUs.
> 
> And does it run one image of Linux? Or more images each 
> on few cpus?
> 
> How do they solve problem with spinlock livelocks?
> 
> If time-spent-outside-spinlock/time-spent-in-spinlock < 
> number-of-cpus, the spinlock livelock may happen --- 
> this condition is not true normally with 2 or 4 cpus, 
> but for that high amount of cpus, there is a danger.

Lets say time-spent-outside-spinlock == time-spent-in-spinlock and
number-of-cpus == 2.

1 < 2 , so it should livelock according to you...

...but afaict this should work okay. Even if spinlocks are very
unfair, as long as time-outside and time-inside comes in big chunks,
it should work.

If you are unlucky, one cpu may stall for a while, but... I see no
livelock.

-- 
Thanks for all the (sleeping) penguins.
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