Re: [Xen-devel] Singleshot timer firing late

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.05.14 at 12:42, <ross.lagerwall@xxxxxxxxxx> wrote:
> While investigating a separate timer issue, I noticed that, in the
> absence of other timers/factors, singleshot timers in Xen always fire
> 50us late (the timer slop amount).
> 
> From what I can see, this behavior was introduced by 116d62ddfd11
> ("timers: Simplify implementation logic.").  Before that, a similar
> issue was fixed by 7e3e35eed67b ("Fix one timer range issue").
> 
> I have attached an RFC patch to program the timer to the nearest
> deadline and then fire any timers up to 50us after that.  This is in
> contrast with the previous behavior which would always program the
> timer 50us after the nearest deadline.

While the patch may certainly do what you want, you don't give
enough explanation of why this is what every one wants. Plus
firing timers early is precisely what we _do not_ want in general.
Furthermore, if this 50ms slop is of concern to you, using the
corresponding command line option to shrink or eliminate it would
be the first thing to try anyway - that's why the command line
option was added after all.

Jan


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