Re: [patch 4 15/22] timer: Remove slack leftovers

From	"Jason A. Donenfeld" <Jason@zx2c4.com>
Newsgroups	linux.kernel
Subject	Re: [patch 4 15/22] timer: Remove slack leftovers
Date	2016-07-23 01:00 +0200
Message-ID	<rXRAe-3sk-25@gated-at.bofh.it> (permalink)
References	<rR8Pv-419-7@gated-at.bofh.it> <rR8Pv-419-27@gated-at.bofh.it> <rXGYa-5de-7@gated-at.bofh.it> <rXInf-6hr-1@gated-at.bofh.it> <rXKp3-7uV-17@gated-at.bofh.it>
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On Fri, Jul 22, 2016 at 5:18 PM, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> Hi Thomas,
>
> On Fri, Jul 22, 2016 at 3:04 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>>
>> Well, this really depends on the TIMEOUT value you have. The code now does
>> implicit batching for larger timeouts by queueing the timers into wheels with
>> coarse grained granularity. As long as your new TIMEOUT value ends up in the
>> same bucket then that's equivalent to the slack thing.
>>
>> Can you give me a ballpark of your TIMEOUT value?
>
> Generally either 5 seconds, 10 seconds, or 25 seconds.
>
> Are these okay? Is the 25 case substantially different from the 5 case?

I suppose, anyway, it's easy enough just to provide my own coalescing
function. Actually, I'd rather have it batch timers to fire earlier
rather than later, in my case. So, I can do something like this to
round down to the nearest ~ quarter of a second:

    static inline unsigned long slack_time(unsigned long time)
    {
       return time & ~(BIT_MASK(ilog2(HZ / 4) + 1) - 1);
    }

    mod_timer(&timer, slack_time(jiffies + TIMEOUT));

This seems to do roughly what I want.

Jason

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Re: [patch 4 15/22] timer: Remove slack leftovers "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-07-22 13:40 +0200
  Re: [patch 4 15/22] timer: Remove slack leftovers Thomas Gleixner <tglx@linutronix.de> - 2016-07-22 15:10 +0200
    Re: [patch 4 15/22] timer: Remove slack leftovers "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-07-22 17:20 +0200
      Re: [patch 4 15/22] timer: Remove slack leftovers "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-07-23 01:00 +0200

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