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Message-ID: <47095967.8060608@gelato.unsw.edu.au> Date: Mon, 08 Oct 2007 08:10:47 +1000 From: Joshua Root <jmr@...ato.unsw.edu.au> To: Ingo Molnar <mingo@...e.hu> CC: "Alan D. Brunelle" <Alan.Brunelle@...com>, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, linux-kernel@...r.kernel.org, btrace <linux-btrace@...r.kernel.org>, Jens Axboe <jens.axboe@...cle.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: Linux Kernel Markers - performance characterization with large IO load on large-ish system Ingo Molnar wrote: > actually, the pure marker overhead seems to be a regression: > > Kernel Options Min val Avg val Max val Std Dev >> - markers - bt cfg 15.349127 16.169459 16.372980 0.184417 >> + markers - bt cfg 15.280382 16.202398 16.409257 0.191861 > > why isnt the marker near zero-cost as it should be? (as long as they are > enabled but are not in actual use) 2% increase is _ALOT_. The increase in the mean is actually 0.033, or 0.2%. > So there's something wrong going on - either markers have unacceptably > high cost, or the measurement is not valid. The third option is that the measurement just needs to be done more times. The standard error in the mean for the + markers case is 0.191861 / sqrt(10) = 0.061, which is twice the size of the difference being measured. -- Joshua Root, jmr AT gelato.unsw.edu.au http://www.gelato.unsw.edu.au - 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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