Gilles Chanteperdrix wrote: > Paul wrote: >> Hi Giles >> >> On Tuesday 27 January 2009, Gilles Chanteperdrix wrote: >>> So, the question is: are there people around who either: >>> - need FPU support for kernel-space real-time threads; >>> - do not want to pay the price of a trap when using the FPU in user-space. >> One application that I work on uses floating point math in kernel space, but >> it is a constant source of problems - Being forced to migrate to user space >> would be a welcome move.. The only question is how much of an overhead does >> the trap incur ? > > The answer probably depends on the machine. You can probably estimate it > for x86 by using rdtsc in well chosen places. What you need to measure > is the time between the fpu fault in user-space and the beginning of the > fpu fault handler in kernel-space, then the time between the end of the > fpu fault handler and the return to user-space. >
Enabling the I-pipe tracer would help in determining how many cycles are burnt from early trap handling back to the supervisor exit point; if you do this, you may want to keep IPIPE_DEBUG_CONTEXT off, since this adds some overhead on low end hw. user/supervisor transition time would have to be added as well, but this is likely not the most significant portion of the overhead. -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
