On Tue, 2011-06-21 at 16:05 +0200, Gilles Chanteperdrix wrote: > On 06/21/2011 03:15 PM, Philippe Gerum wrote: > > On Tue, 2011-06-21 at 15:05 +0200, roderik.wildenb...@manroland.com > > wrote: > >>> But more importantly, since, the time when we print the result is so > >>> imprecise, some variations are normal, so, chances are that the 2% > >>> variation is normal. > >>> > >> > >> Ok. Here is a switchtest with Xenomai 2.4.9 on PPC-Kernel 2.4.25 and > >> indeed fluctuation is again about 2%. > >> But the number of context switches is just about 25% of switchtest from > >> Xeno 2.5.6 on a PPC-2.6.34. Did you change the tasks period from 2.4.9 to > >> 2.5.6? > >> So, if the gurus say this variation is within the normal bandwidth it is > >> ok for me. > > > > The number of switches is related to the number of tasks running in this > > test, nofpu reduces this number. So that is ok. The problem with this > > test is that switches/sec values are sampled by a regular linux thread > > which nanosleeps, so at least over 2.4, the delay is not accurate. So > > the number of switches observed can't be either. > > The task which nanosleeps does not really sample the number of context > switches, it is part of the context switches chain, and simply prints > the number when it sees that the last time the number was printed is > more than 1s ago. So, how many context switches happen depends greatly > on how many time the context switches chain passed by this task, and so > is not regular.
This is why the sleeper actually samples somehow, polling then printing the switch count from the driver based on a 1ms period it runs, given that the scheduling chain should be reasonably fixed. Granted, this cannot be precise at all in any case. > > The switchtest code also changed between 2.4 > and 2.6, which is why you > can not compare the numbers. > > Pay no attention to the number of context switches. All which matters is > that this number increase over time, this is why we print them. > And as a matter of fact, this is the good way to quickly detect the kernel 2.4 issue we have. -- Philippe. _______________________________________________ Xenomai-help mailing list Xenomai-help@gna.org https://mail.gna.org/listinfo/xenomai-help
