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Date: Sun, 8 Feb 2009 21:27:48 -0800 From: Arjan van de Ven <arjan@...radead.org> To: Frederic Weisbecker <fweisbec@...il.com> Cc: Cornelia Huck <cornelia.huck@...ibm.com>, lkml <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] fastboot: keep at least one thread per cpu during boot On Mon, 9 Feb 2009 04:48:27 +0100 Frederic Weisbecker <fweisbec@...il.com> wrote: > Async threads are created and destroyed depending on the number of > jobs in queue. It means that several async threads can be created for > a specific batch of work, then the threads will die after the > completion of this batch, but they could be needed just after this > completion for another batch of work. During the boot, such > repetitive thread creations can be wasteful, that's why this patch > proposes to keep at least one thread per cpu (if they already have > been created once). Such a threshold of threads kept alive will > prevent from a part of the thread creation overhead. This threshold > will be dropped one the system_state switches from SYSTEM_BOOTING to > SYSTEM_RUNNING. I'm not very fond of this to be honest; at least during boot there's enough activity, and the time is so short (that's the point of the parallel stuff!) that this will not kick in to make a difference; specifically, every boot I've seen the number of threads is highest near the end, and also the total kernel boot time is below 1.5 seconds or so, not long enough for the threads to die. Creating a thread is *CHEAP*. Really really cheap. You can do 100 thousands/second on even a modest CPU. If you have a high frequency of events, you don't want this, sure, and that is why there is a one second delay to give opportunity for reuse... but really.... Now, if async function calls get used more, I can see the point of always keeping one thread alive, just for both performance and VM low memory issues; but that's not what your patch is doing. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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