On Fri, 2015-07-17 at 08:40 +1000, Benjamin Herrenschmidt wrote: > On Wed, 2015-07-15 at 17:37 +1000, Michael Ellerman wrote: > > To call do_syscall_trace_enter() we need pt_regs in r3, but we don't need > > to recalculate it based on r1, it's already in r9. > > > > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > > Is there any performance difference ?
No. I'm not going to bother measuring it :) > I find the addi a bit more robust in case the code gets moved around or > the "previous" code gets changed to either not use r9 or clobber it, > which would have the potential to > introduce a subtle bug ... Yeah true. There is an "invariant" in that entry code that r9 contains pt_regs, you can see for example the DTL code goes to pains to ensure it puts pt_regs back in r9 after it clobbers it. As does the current syscall_dotrace. But looking closer I don't see where we actually use that (prior to this patch). So yeah I'll drop this and send a clean up to just get rid of all the r9 reloading. cheers _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
