On Wed, May 23, 2018 at 11:05:34AM -0700, John Stultz wrote: > On Wed, May 23, 2018 at 4:33 AM, Miroslav Lichvar <mlich...@redhat.com> wrote: > > This removes a hidden non-deterministic delay in setting of the > > frequency and allows an extremely tight control of the system clock > > with update rates close to or even exceeding the kernel HZ.
> I feel like we tried this years back, but had to revert it. But its > been awhile. Am I confusing things? IIRC we only talked about doing this. Before the recent changes in timekeeping, namely c2cda2a5 (Don't align NTP frequency adjustments to ticks), it wouldn't make much sense. There would still be a hidden delay, it would just be negative (from the applications point of view). > > - /* Check if there's really nothing to do */ > > - if (offset < real_tk->cycle_interval) > > - goto out; > > - > > Apologies again, as I don't have a lot of context here these days, but > this could mean we end up doing unnecessary work on every > update_wall_time, no? I'm not sure. If I understand it correctly, update_wall_time() is normally not called more than once per tick. Only when an update is late and it happens to include the next tick, the subsequent call might be unnecessary, right? > Would a "force" flag be better to pass to update_wall_time() to only > avoid the short-cut in the non-adjtimex case? Yes, that makes sense. Thanks, -- Miroslav Lichvar
