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From: Cort Dougan <cort@fsmlabs.com>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Ingo Molnar <mingo@elte.hu>, Rik van Riel <riel@conectiva.com.br>,
	Andries Brouwer <aebr@win.tue.nl>,
	William Lee Irwin III <wli@holomorphy.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK
Date: Wed, 18 Sep 2002 11:35:51 -0600	[thread overview]
Message-ID: <20020918113551.A654@host110.fsmlabs.com> (raw)
In-Reply-To: <Pine.LNX.4.44.0209181026550.1230-100000@home.transmeta.com>; from torvalds@transmeta.com on Wed, Sep 18, 2002 at 10:30:35AM -0700

It's also not a bad idea to sometimes say "Linux cannot do that".  Trying
to make the system do _everything_ will result in it doing many things very
poorly.

} Again, you're talking about entirely theoretical numbers that have no 
} relevance for real life. 
} 
} Sure, you can do that. But a real life box? Nope.
} 
} >						 Or in 1.25 hours
} > on an 8-way box. And then we are back to step #1: trying to pass over
} > already allocated PIDs by destroying the contents of the L1 and L2 cache
} > once for each allocated PID passed.
} 
} So? It happens very rarely, and..
} 
} >			 Sure, with 2 billion PIDs space that
} > averages out, but it's an algorithm with a very nasty worst-case behavior,
} > which is not so hard to trigger.
} 
} ... the worst-case-behaviour is basically impossible to trigger with any 
} real load. 
} 
} The worst case does not happen for "100k threads" like you've made it 
} sound like.
} 
} The worst case happens for "100k threads consecutive in the pid space".
} 
} Which means that not only do you have to roll over, you have to roll over 
} with a humungous number of threads _still_ occupying their old consecutive 
} positions when you roll over.
} 
} I repeat: you're making up schenarios that simply have no relevance to 
} real life.
} 
} 		Linus
} 
} -
} To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
} the body of a message to majordomo@vger.kernel.org
} More majordomo info at  http://vger.kernel.org/majordomo-info.html
} Please read the FAQ at  http://www.tux.org/lkml/

  reply	other threads:[~2002-09-18 17:33 UTC|newest]

Thread overview: 82+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-09-17 23:06 [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK Ingo Molnar
2002-09-18  0:22 ` William Lee Irwin III
2002-09-18  1:27   ` David S. Miller
2002-09-18  2:22     ` William Lee Irwin III
2002-09-18 10:11   ` Ingo Molnar
2002-09-18 14:28     ` William Lee Irwin III
2002-09-18 12:32 ` Andries Brouwer
2002-09-18 12:56   ` Ingo Molnar
2002-09-18 16:17     ` Linus Torvalds
2002-09-18 16:46       ` Ingo Molnar
2002-09-18 16:57       ` Ingo Molnar
2002-09-18 18:28     ` Andries Brouwer
2002-09-18 18:27       ` William Lee Irwin III
2002-09-18 19:00       ` Ingo Molnar
2002-09-18 20:11         ` Andries Brouwer
2002-09-18 20:29           ` William Lee Irwin III
2002-09-18 21:15             ` Andries Brouwer
2002-09-19  3:05               ` Ingo Molnar
2002-09-19 13:11                 ` Andries Brouwer
2002-09-21 12:56                   ` quadratic behaviour Andries Brouwer
2002-09-21 17:06                     ` Linus Torvalds
2002-09-21 17:35                       ` William Lee Irwin III
2002-09-21 17:49                       ` Ingo Molnar
2002-09-21 17:46                         ` William Lee Irwin III
2002-09-18 14:49   ` [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK William Lee Irwin III
2002-09-18 15:01     ` Cort Dougan
2002-09-18 15:33       ` Ingo Molnar
2002-09-18 15:31         ` yodaiken
2002-09-18 15:35         ` Cort Dougan
2002-09-18 15:37       ` Rik van Riel
2002-09-18 15:50       ` Alan Cox
2002-09-18 18:31     ` Andries Brouwer
2002-09-18 18:32       ` William Lee Irwin III
2002-09-18 16:15   ` Linus Torvalds
2002-09-18 16:32     ` Rik van Riel
2002-09-18 16:48       ` Linus Torvalds
2002-09-18 17:31         ` Ingo Molnar
2002-09-18 21:46         ` Rogier Wolff
2002-09-18 16:41     ` Ingo Molnar
2002-09-18 16:45       ` William Lee Irwin III
2002-09-18 16:59         ` Linus Torvalds
2002-09-18 17:36         ` Ingo Molnar
2002-09-18 17:36           ` William Lee Irwin III
2002-09-18 17:46             ` Linus Torvalds
2002-09-18 17:47               ` William Lee Irwin III
2002-09-18 17:59             ` Ingo Molnar
2002-09-18 17:50               ` William Lee Irwin III
2002-09-18 18:07                 ` Ingo Molnar
2002-09-19 19:27           ` Martin Mares
2002-09-17 15:31             ` Pavel Machek
2002-09-19 20:07             ` Richard B. Johnson
2002-09-18 16:46     ` Rik van Riel
2002-09-18 16:53       ` Linus Torvalds
2002-09-18 17:00         ` Rik van Riel
2002-09-18 17:16           ` Linus Torvalds
2002-09-18 17:28             ` Ingo Molnar
2002-09-18 17:38           ` Ingo Molnar
2002-09-18 17:24         ` Ingo Molnar
2002-09-18 17:30           ` Linus Torvalds
2002-09-18 17:35             ` Cort Dougan [this message]
2002-09-18 17:43               ` Rik van Riel
2002-09-18 17:48               ` Martin J. Bligh
2002-09-18 17:57                 ` Cort Dougan
2002-09-18 18:08                   ` Martin J. Bligh
2002-09-18 18:28                     ` Ingo Molnar
2002-09-18 18:33                       ` Linus Torvalds
2002-09-18 18:51                         ` Ingo Molnar
2002-09-18 18:56                           ` interruptible_sleep_on_timeout() and signals Imran Badr
2002-09-19  7:16                             ` David Woodhouse
2002-09-18 19:53                       ` [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK Martin J. Bligh
2002-09-22  0:34                   ` Andrea Arcangeli
2002-09-22 10:02                     ` Ingo Molnar
2002-09-22 15:27                       ` Andrea Arcangeli
2002-09-18 18:02               ` Ingo Molnar
2002-09-18 17:58                 ` Cort Dougan
2002-09-18 18:14                   ` Ingo Molnar
2002-09-18 17:54             ` Alan Cox
2002-09-18 17:54             ` Ingo Molnar
2002-09-18 18:00               ` yodaiken
2002-09-18 18:21                 ` Ingo Molnar
2002-09-18 18:33                   ` yodaiken
2002-09-18 16:55     ` Alan Cox

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