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Date: 9 Jun 2015 01:39:30 -0400 From: "George Spelvin" <linux@...izon.com> To: linux@...izon.com, tglx@...utronix.de Cc: linux-kernel@...r.kernel.org, peterz@...radead.org, viresh.kumar@...aro.org Subject: Re: [patch 2/7] timer: Remove FIFO guarantee Thomas Gleixner wrote: > It does. Depending on when you enqueue the timer because the thing is > calculated from the delta (expires - jiffies). Ah, right. If slack > 0, the slack amount is absolute and the rounding will be consistent. But if slack < 0, which is the default, it's a percentage of remaining jiffies. Since slack only delays timeouts, an earlier-scheduled timeout could easily be delayed more. (There are only six calls to set_timer_slack() to change the default to something positive in the kernel.) >> I'm not disagreeing with the change, but it's not clear to me that >> it's as safe as you think. > After thinking more about it, I'm even more sure that any code which > relies on the FIFO "guarantee" is broken today. Indeed, I am completely convinced. All I might request is a reassignment of blame in the commit message. Thank you for your comments on my other blue-sky ideas, too. I need to look into why we're using wheels, and what the point is. How much of an advantage do they have over an efficient priority queue like a pairing heap? -- 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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