Am 20.01.2011 11:01, schrieb Bernd Mueller: > Henry Vermaak wrote: >> On 20/01/11 08:20, Michael Schnell wrote: >>> On 01/19/2011 05:13 PM, Henry Vermaak wrote: >>>> >>>> it's really expensive to trap the illegal instructions and emulate >>>> them. >>> AFAIK, the trapping is done by the ARM CPU, anyway, providing the >>> emulation functions just costs some memory, but of course it's even >>> slower and more intrusive than directly calling an FPU emulation >>> function in user space. >> >> No, the cpu generates an exception for every illegal fpu operation, >> which gets trapped by the kernel. The kernel then has to catch this >> instruction and perform it by emulating the _whole_ fpu. This, >> together with the exception handling causes the bad performance. Look >> at the code in arch/arm/nwfpe if you're interested. > > three years ago, I compared an OABI kernel with double precision > Netwinder FPE emulation against softfloat and the softfloat variant was > about 2 until 10 times faster, depending on the floating point > instructions.
The trapping is done in hardware but it still takes a lot of time, it's a context switch after all. _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
