Re: [systemd-devel] Reason for setting runqueue to IDLE priority and side effects if this is changed?
On Wed, 15.07.15 17:30, Hoyer, Marko (ADITG/SW2) (mho...@de.adit-jv.com) wrote: > Systemd v211 added the running queue as deferred event source to the > event handling with priority IDLE. So dbus requests are preferred > over job execution. The reverse order effect is simply because the > run queue is more a stack than a queue. All of the observed behavior > could be explained I guess. > > So long story in advance. I've now two questions: > - Am I causing any critical side effects when I'm increasing the run > queue priority so that it is higher than the one of the dbus > handling (which is NORMAL)? First tests showed that I can get back > exactly the behavior we had before with that. The idea was that if the user wants us to undo some operation, we better operate on that first, before we execute the job he might want to undo. Hence dbus requests get priority. But other than that I don't see how this would be a problem. > - Might it still happen that situations are happening where the jobs > are reordered even though I'm increasing the priority? Well, we currently say that the order in which jobs are dispatched if multiple are runnable (where "runnable" means "all deps satisfied") is undefined. I'd be willing to add a new unit setting to unit files that would allow altering the order in which jobs are dispatched if multiple are runnable. For example, we could add a new value Priority= which could allow altering the order in which runnable jobs are dispatched. This run queue (which is actually a stack right now...) would then become a priority queue. Such a ptahc would probably not be too difficult, given that we already have a prioq abstract data structure in systemd. > - Is there any other good solution ensuring the order of job execution? No yet, sorry. Would be happy to take a patch implementing what I suggested above! Lennart -- Lennart Poettering, Red Hat ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Reason for setting runqueue to IDLE priority and side effects if this is changed?
> > > > Up to v206, the behavior of systemd was the following one: > > -- > > - the starter sends out a start request of a bench of applications > (he requests a sequence of unit starts) > > If you want to control order of execution yourself, why do you not wait > for each unit to start before submitting next request? The synchronization point is not 'Unit started' but 'Job started'. I'm searching for a good solution to detect that. > > So long story in advance. I've now two questions: > > - Am I causing any critical side effects when I'm increasing the run > queue priority so that it is higher than the one of the dbus handling > (which is NORMAL)? First tests showed that I can get back exactly the > behavior we had before with that. > > > > - Might it still happen that situations are happening where the jobs > are reordered even though I'm increasing the priority? > > > > - Is there any other good solution ensuring the order of job > execution? > > > > systemd never promised anything about relative order of execution > unless there is explicit dependency between units. So good solution is > to put dependency in unit definitions. submit the whole bunch at once > and let systemd sort the order. Understood and agreed ;) Dependency is not an option because the synchronization point is not 'Unit Started' but 'Job kicked off' for the sequence. The sync point 'Unit Started' is need for "real" dependencies. However, has anyone an opinion on the first idea? (increasing the priority) I'd be interested in side effects caused by this modification. Thx, Marko ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] Reason for setting runqueue to IDLE priority and side effects if this is changed?
В Wed, 15 Jul 2015 17:30:53 + "Hoyer, Marko (ADITG/SW2)" пишет: > Hi all, > > jumping from systemd 206 to systemd 211 we were faced with some issue, which > are finally caused by a changed main loop priority of the job execution. > > Our use case is the following one: > -- > While we are starting up the system, a so called application starter is > bringing up a set of applications at a certain point in a controlled way by > requesting systemd via dbus to start respective units. The reason is that we > have to take care for applications internal states as synchronization points > and for better meeting timing requirements of certain applications in a > generic way. I told the story once before in another post about watchdog > observation in state "activating". However ... > > Up to v206, the behavior of systemd was the following one: > -- > - the starter sends out a start request of a bench of applications (he > requests a sequence of unit starts) If you want to control order of execution yourself, why do you not wait for each unit to start before submitting next request? > - it seems that systemd is working of the sequence exactly as it was > requested one by one in the same order > > Systemd v211 shows a different behavior: > > - the starter sends out a bench of requests > - the job execution of the first job is significantly delayed (we have a > system under stress, high CPU load at that time) > - suddenly, system starts working of the jobs but now in reverse order > - depending on the situation, it might happen that a complete bench of > scheduled jobs are reverse ordered, sometimes two or more sub benches of jobs > are executed in the reverse order (the jobs in each bench are reverse ordered) > > I found that the system behavior with systemd v206 was only accidently the > expected one. The reason was that in this version the run queue dispatching > was a fixed part of the main loop located before the dispatching of the > events. This way, it gained higher priority than the dbus request handling. > One jobs was requested via dbus. Once the dbus job request was dispatched, > it's been worked off immediately the next round of the mainloop. Then the > next dbus request was dispatched and so on ... > > Systemd v211 added the running queue as deferred event source to the event > handling with priority IDLE. So dbus requests are preferred over job > execution. The reverse order effect is simply because the run queue is more a > stack than a queue. All of the observed behavior could be explained I guess. > > So long story in advance. I've now two questions: > - Am I causing any critical side effects when I'm increasing the run queue > priority so that it is higher than the one of the dbus handling (which is > NORMAL)? First tests showed that I can get back exactly the behavior we had > before with that. > > - Might it still happen that situations are happening where the jobs are > reordered even though I'm increasing the priority? > > - Is there any other good solution ensuring the order of job execution? > systemd never promised anything about relative order of execution unless there is explicit dependency between units. So good solution is to put dependency in unit definitions. submit the whole bunch at once and let systemd sort the order. ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
[systemd-devel] Reason for setting runqueue to IDLE priority and side effects if this is changed?
Hi all, jumping from systemd 206 to systemd 211 we were faced with some issue, which are finally caused by a changed main loop priority of the job execution. Our use case is the following one: -- While we are starting up the system, a so called application starter is bringing up a set of applications at a certain point in a controlled way by requesting systemd via dbus to start respective units. The reason is that we have to take care for applications internal states as synchronization points and for better meeting timing requirements of certain applications in a generic way. I told the story once before in another post about watchdog observation in state "activating". However ... Up to v206, the behavior of systemd was the following one: -- - the starter sends out a start request of a bench of applications (he requests a sequence of unit starts) - it seems that systemd is working of the sequence exactly as it was requested one by one in the same order Systemd v211 shows a different behavior: - the starter sends out a bench of requests - the job execution of the first job is significantly delayed (we have a system under stress, high CPU load at that time) - suddenly, system starts working of the jobs but now in reverse order - depending on the situation, it might happen that a complete bench of scheduled jobs are reverse ordered, sometimes two or more sub benches of jobs are executed in the reverse order (the jobs in each bench are reverse ordered) I found that the system behavior with systemd v206 was only accidently the expected one. The reason was that in this version the run queue dispatching was a fixed part of the main loop located before the dispatching of the events. This way, it gained higher priority than the dbus request handling. One jobs was requested via dbus. Once the dbus job request was dispatched, it's been worked off immediately the next round of the mainloop. Then the next dbus request was dispatched and so on ... Systemd v211 added the running queue as deferred event source to the event handling with priority IDLE. So dbus requests are preferred over job execution. The reverse order effect is simply because the run queue is more a stack than a queue. All of the observed behavior could be explained I guess. So long story in advance. I've now two questions: - Am I causing any critical side effects when I'm increasing the run queue priority so that it is higher than the one of the dbus handling (which is NORMAL)? First tests showed that I can get back exactly the behavior we had before with that. - Might it still happen that situations are happening where the jobs are reordered even though I'm increasing the priority? - Is there any other good solution ensuring the order of job execution? Hope someone has some useful feedback. Thx in advance. Marko Hoyer Advanced Driver Information Technology GmbH Software Group II (ADITG/SW2) Robert-Bosch-Str. 200 31139 Hildesheim Germany Tel. +49 5121 49 6948 Fax +49 5121 49 6999 mho...@de.adit-jv.com ADIT is a joint venture company of Robert Bosch GmbH/Robert Bosch Car Multimedia GmbH and DENSO Corpoation Sitz: Hildesheim, Registergericht: Amtsgericht Hildesheim HRB 3438 Geschaeftsfuehrung: Wilhelm Grabow, Katsuyoshi Maeda ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
