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Date: Mon, 12 Dec 2011 15:18:15 -0800 From: Steve Calfee <stevecalfee@...il.com> To: Alan Stern <stern@...land.harvard.edu> CC: USB list <linux-usb@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, Kernel development list <linux-kernel@...r.kernel.org> Subject: Re: Busy-waiting with interrupts disabled On 12/12/11 14:12, Alan Stern wrote: > How long is it okay to busy-wait with interrupts disabled? Are there > any clear-cut guidelines? > > My feeling is that for ordinary desktop use, 1-2 ms should be about the > limit, but other people may feel differently. (There's one spot in > ehci-hcd where the delay can last up to 250 ms, which does seem rather > excessive. Fortunately it never takes that long unless the hardware is > broken.) > This is a very subjective issue, as to how much is too much. Keep in mind that when we had 1 MIP computers a delay of 1 to 2 ms would "waste" from 1000 to 2000 potential instructions. With 3 gighz processors, the potential waste jumps to 3,000,000 to 6,000,000 instructions. I know that clock speed does not equal mips and that most processors spend most of their time waiting for memory, but still, the waste increases with processor speed. Regards, Steve -- 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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