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    SubjectRe: [patch 13/20] timer: Switch to a non cascading wheel
    On Tue, Jun 14, 2016 at 1:42 PM, Peter Zijlstra <peterz@infradead.org> wrote:
    > On Tue, Jun 14, 2016 at 08:05:49PM +0200, Thomas Gleixner wrote:
    >> On Tue, 14 Jun 2016, Arjan van de Ven wrote:
    >>
    >> > evaluating a 120 hours timer ever 37 hours to see if it should fire...
    >> > not too horrid.
    >>
    >> Well that thing is doing weird stuff anyway:
    >>
    >> swapper 0 [001] 1789995.305532: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4850639994 [timeout=108000000]
    >> ssh 3870 [001] 1790025.284704: timer:timer_cancel: timer=0xffff8800c8346920
    >> ssh 3870 [001] 1790025.284707: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4742722493 [timeout=75000]
    >> swapper 0 [001] 1790025.330514: timer:timer_cancel: timer=0xffff8800c8346920
    >> swapper 0 [001] 1790025.330515: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4850647504 [timeout=108000000]
    >> ssh 3870 [001] 1790055.307058: timer:timer_cancel: timer=0xffff8800c8346920
    >> ssh 3870 [001] 1790055.307060: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4742730003 [timeout=75000]
    >> swapper 0 [001] 1790055.352146: timer:timer_cancel: timer=0xffff8800c8346920
    >>
    >> And that goes on forever. 2834 such sequences for this particular timer
    >> instance in 4.5 hours. 90000 sequences total for all timers related to
    >> death_by_timeout in 4.5 hours
    >>
    >> No idea what this is doing and why the heck it nees a 120 hour timeout ....
    >
    > So it moves that timer on every packet for that TCP connection stream,
    > provided the expiration is at least 1 second behind.
    >
    > If the stream hasn't had a packet in 5 days (see previous email), then
    > the connection state is destroyed.
    >
    > Its been too long since I've read the TCP RFCs, but I can imagine
    > changing this will upset people.
    >

    Original TCP RFCs tell timeout is infinite ;)

    Practically, conntrack has a 5 days timeout, but I really doubt anyone
    expects an idle TCP flow to stay 'alive' when nothing is sent for 5
    days.

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