Re: [dpdk-dev] [PATCH 1/3] timer: inform periodic timers of multiple expiries

[Olivier Matz <olivier.matz@6wind.com>]

Hi Bruce,

On Wed, 31 May 2017 10:16:19 +0100, Bruce Richardson <bruce.richardson@intel.com> wrote:
> if timer_manage is called much less frequently than the period of a
> periodic timer, then timer expiries will be missed. For example, if a timer
> has a period of 300us, but timer_manage is called every 1ms, then there
> will only be one timer callback called every 1ms instead of 3 within that
> time.
> 
> While we can fix this by having each function called multiple times within
> timer-manage, this will lead to out-of-order timeouts, and will be slower
> with all the function call overheads - especially in the case of a timeout
> doing something trivial like incrementing a counter. Therefore, we instead
> modify the callback functions to take a counter value of the number of
> expiries that have passed since the last time it was called.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com> 

Sorry, it's probably a bit late to react. If it's too late, nevermind.
I'm not really convinced that adding another argument to the callback
function is the best solution.

Invoking the callbacks several times would result in a much smaller patch
that does not need a heavy ABI compat.

I'm not sure the function call overhead is really significant in that
case. I'm not sure I understand your point related to out-of-order timeouts,
nor I see why this patchset would behave better.

About the problem itself, my understanding was that the timer manage
function has to be called frequently enough to process the timers.


Olivier