On Wednesday 18 May 2005 17:20, Bodo Stroesser wrote: > Jeff Dike wrote: > > On Wed, May 18, 2005 at 11:47:23AM +0200, Bodo Stroesser wrote: > >>I also thought about not saving FP-regs on each kernel entry. But if you > >> do this optimization, you need to save / restore FP-regs on switch_to. > >> Also you need to get the FP-regs when setting up a signal-handler > >> stackframe. And they > >>have to be restored on sys_(rt_)sigreturn from the values found in the > >>stackframe. > > > > True, but these are much less frequent than kernel entries/exits. > > Yes, so it makes sense to optimize this for i386 and x86_64. > > On s390, I'm not sure, what to do. Using s390's PTRACE_PEEK/POKEUSR_AREA > UML can read or write all regs including FP in a single ptrace call. > So, the change would speed up that call a bit, but would that be enough > to pay the cost of additional ptrace calls in switch_to or signal handling? I think no, because doing a syscall is probably more costly than copying some bytes, however it depends on the relative frequency. Doing a benchmark would probably be the better thing to do. -- Paolo Giarrusso, aka Blaisorblade Skype user "PaoloGiarrusso" Linux registered user n. 292729 http://www.user-mode-linux.org/~blaisorblade
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