Messages in this thread | | | Date | Thu, 1 Oct 2015 16:13:44 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v7 06/11] nohz: task_isolation: allow tick to be fully disabled |
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On Thu, 1 Oct 2015, Frederic Weisbecker wrote: > On Mon, Sep 28, 2015 at 04:40:56PM -0400, Andy Lutomirski wrote: > > On Mon, Sep 28, 2015 at 11:17 AM, Chris Metcalf <cmetcalf@ezchip.com> wrote: > > > While the current fallback to 1-second tick is still helpful for > > > maintaining completely correct kernel semantics, processes using > > > prctl(PR_SET_TASK_ISOLATION) semantics place a higher priority on > > > running completely tickless, so don't bound the time_delta for such > > > processes. In addition, due to the way such processes quiesce by > > > waiting for the timer tick to stop prior to returning to userspace, > > > without this commit it won't be possible to use the task_isolation > > > mode at all. > > > > > > Removing the 1-second cap was previously discussed (see link > > > below) and Thomas Gleixner observed that vruntime, load balancing > > > data, load accounting, and other things might be impacted. > > > Frederic Weisbecker similarly observed that allowing the tick to > > > be indefinitely deferred just meant that no one would ever fix the > > > underlying bugs. However it's at least true that the mode proposed > > > in this patch can only be enabled on a nohz_full core by a process > > > requesting task_isolation mode, which may limit how important it is > > > to maintain scheduler data correctly, for example. > > > > What goes wrong when a task enables this? Presumably either tasks > > that enable it experience problems or performance issues or it should > > always be enabled. > > We need to make the scheduler resilient to 0Hz tick. Currently it doesn't > even correctly support 1Hz or any dynticks behaviour that isn't idle.
Rik has started to work on this. No idea what the status of that is.
Thanks,
tglx
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