Joakim Tjernlund <Joakim.Tjernlund@xxxxxxxxxxxx> writes: > On Fri, 2019-03-29 at 22:26 +1100, Michael Ellerman wrote: >> From: Diana Craciun <diana.craciun@xxxxxxx> >> >> commit ebcd1bfc33c7a90df941df68a6e5d4018c022fba upstream. >> >> Implement the barrier_nospec as a isync;sync instruction sequence. >> The implementation uses the infrastructure built for BOOK3S 64. >> >> Signed-off-by: Diana Craciun <diana.craciun@xxxxxxx> >> [mpe: Split out of larger patch] >> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > > What is the performanc impact of these spectre fixes? I've not seen any numbers from anyone. It will depend on the workload, it's copy to/from user that is most likely to show an impact. We have a context switch benchmark in tools/testing/selftests/powerpc/benchmarks/context_switch.c. Running that with "--no-vector --no-altivec --no-fp --test=pipe" shows about a 2.3% slow down vs booting with "nospectre_v1". > Can I compile it away? You can't actually, but you can disable it at runtime with "nospectre_v1" on the kernel command line. We could make it a user selectable compile time option if you really want it to be. cheers
