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Date: Mon, 16 Jul 2007 09:06:10 +0200 From: Ingo Molnar <mingo@...e.hu> To: James Bruce <bruce@...rew.cmu.edu> Cc: Thomas Gleixner <tglx@...utronix.de>, Roman Zippel <zippel@...ux-m68k.org>, Mike Galbraith <efault@....de>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrea Arcangeli <andrea@...e.de>, Andi Kleen <andi@...stfloor.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, Arjan van de Ven <arjan@...radead.org>, Chris Wright <chrisw@...s-sol.org> Subject: Re: [PATCH] CFS: Fix missing digit off in wmult table * James Bruce <bruce@...rew.cmu.edu> wrote: > While we're at it, isn't the comment above the wmult table incorrect? > The multiplier is 1.25, meaning a 25% change per nice level, not 10%. yes, the weight multiplier 1.25, but the actual difference in CPU utilization, when running two CPU intense tasks, is ~10%: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 8246 mingo 20 0 1576 244 196 R 55 0.0 0:11.96 loop 8247 mingo 21 1 1576 244 196 R 45 0.0 0:10.52 loop so the first task 'wins' +10% CPU utilization (relative to the 50% it had before), the second task 'loses' -10% CPU utilization (relative to the 50% it had before). so what the comment says is true: * The "10% effect" is relative and cumulative: from _any_ nice level, * if you go up 1 level, it's -10% CPU usage, if you go down 1 level * it's +10% CPU usage. for there to be a ~+10% change in CPU utilization for a task that races against another CPU-intense task there needs to be a ~25% change in the weight. Ingo - 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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