Jamie Lokier wrote: > Avi Kivity wrote: > >>>>> In this case the dyn-tick minimum res will be 1msec. I believe it should >>>>> work ok since this is the case without any dyn-tick. >>>>> >>>>> >>>> Actually minimum resolution depends on host HZ setting, but - yes - >>>> essentially you have the same behaviour of the "unix" timer, plus the >>>> overhead of reprogramming the timer. >>>> >>>> >>> Is this significant? At a high guest HZ, this is could be quite a lot >>> of additional syscalls right? >>> >>> >> At HZ=1000, this adds a small multiple of 1000 syscalls, which is a >> fairly small overhead. >> > > Small, but maybe measurable. > > That overhead could be removed if the dyn-tick code were to > predictively set the host timer into a repeating mode when guests do > actually require a regular tick. > > I'm thinking when it detects it needed a tick a small number of times > in a row, with the same interval, it could set the host timer to > trigger repeatedly at that interval. Then it wouldn't need to reprogram > if that stayed the same (except maybe to correct for drift?) > > If a tick then _wasn't_ required for that interval (i.e. it was > required for less, more, or not at all), then it would have to > reprogram the host timer. If it really mattered, it wouldn't have to > reprogram the host timer when the next required tick is further in the > future or not at all; it would simply be a redundant SIGALRM. In > weird cases that's worthwhile, but I suspect it generally isn't. > >
Yes, good thinking, but this should only be done if it actually impacts something. Reducing overhead from 0.1% to 0.05% is not worthwhile if it introduces extra complexity. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
