On Mon, May 12, 2014 at 02:33:42PM +0200, Michael Kerrisk (man-pages) wrote: > > I'm a proponent of fail hard instead of fail silently and muddle on. > > And while we can fully and correctly return sched_getscheduler() we > > cannot do so for sched_getparam(). > > > > Returning sched_param::sched_priority == 0 for DEADLINE would also break > > the symmetry between sched_setparam() and sched_getparam(), both will > > fail for SCHED_DEADLINE. > > Maybe. But there seems to me to be a problem with your logic here. > (And the symmetry argument seems a weak one to me.) > > I mean, applications that are currently using sched_getscheduler() > will now get back a new policy (SCHED_DEADLINE) that they may not > understand, and so they may break. > > On the other hand, applications that call sched_getparam() will fail > with EINVAL, even though sched_priority has no meaning for > SCHED_DEADLINE (as for the non-real-time policies), and so it would > seem to be harmless to succeed and return a sched_priority of 0 in > this case. It seems to break user-space needlessly, IMHO. > > If anything, I'd have said it would have made more sense to have the > sched_getscheduler() case fail, while having the sched_getparam() case > succeed. (But, I can see the argument for having _both_ cases > succeed.) Hmm,.. maybe. Can we still change this? Again, maybe, there's not really that much userspace that relies on this. In any case, the way I read the little there is on getparam() it seems to imply the only case where it does make sense to call it at all is when sched_getscheduler() returns either SCHED_FIFO or SCHED_RR. And in that sense I suppose the precedent for all other currently available classes to not fail the param call but return 0 should be extended. If only we'd started out with sched_yield()/sched_getparam() etc failing when not !SCHED_FIFO/RR :-)
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