Messages in this thread |  | | Date | 9 Jun 2015 01:39:30 -0400 | From | "George Spelvin" <> | Subject | Re: [patch 2/7] timer: Remove FIFO guarantee |
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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?
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