Messages in this thread | | | Date | Fri, 29 Jun 2012 10:03:27 +0200 | From | Jiri Olsa <> | Subject | Re: [RFC 09/23] x86_64: Store userspace rsp in system_call fastpath |
| |
On Thu, Jun 28, 2012 at 02:08:49PM +0200, Frederic Weisbecker wrote: > On Tue, Jun 19, 2012 at 05:48:00PM +0200, Jiri Olsa wrote: > > hi, > > I'd need help with this change.. basically it works, but I guess > > I could alter the FIXUP_TOP_OF_STACK macro as well, so the rsp is > > not initialized twice in slowpath. > > > > But it seems quite complex.. so not really sure at the moment ;) > > > > ideas? > > > > thanks, > > jirka > > > > --- > > Storing the userspace rsp into the pt_regs struct for the > > system_call fastpath (syscall instruction handler). > > > > Following part of the pt_regs is allocated on stack: > > (via KERNEL_STACK_OFFSET) > > > > unsigned long ip; > > unsigned long cs; > > unsigned long flags; > > unsigned long sp; > > unsigned long ss; > > > > but only ip is actually saved for fastpath. > > > > For perf post unwind we need at least ip and sp to be able to > > start the unwind, so storing the old_rsp value to the sp. > > > > Signed-off-by: Jiri Olsa <jolsa@redhat.com> > > Cc: Borislav Petkov <bp@alien8.de> > > Cc: H. Peter Anvin <hpa@zytor.com> > > Cc: Roland McGrath <roland@hack.frob.com> > > --- > > arch/x86/kernel/entry_64.S | 5 +++++ > > 1 files changed, 5 insertions(+), 0 deletions(-) > > > > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > > index 111f6bb..0444917 100644 > > --- a/arch/x86/kernel/entry_64.S > > +++ b/arch/x86/kernel/entry_64.S > > @@ -516,6 +516,11 @@ GLOBAL(system_call_after_swapgs) > > SAVE_ARGS 8,0 > > movq %rax,ORIG_RAX-ARGOFFSET(%rsp) > > movq %rcx,RIP-ARGOFFSET(%rsp) > > +#ifdef CONFIG_PERF_EVENTS > > + /* We need rsp in fast path for perf post unwind. */ > > + movq PER_CPU_VAR(old_rsp), %rcx > > + movq %rcx,RSP-ARGOFFSET(%rsp) > > +#endif > > Another solution is to set/unset some TIF flag in perf_event_sched_in/out > such that we take the syscall slow path (tracesys) which records every non-scratch > registers. I can see that old_rsp is not saved in pt_regs by SAVE_REST so this may be > something to add in tracesys. > > This way we don't bloat the syscall fastpath with a feature only used by some > developers.
ok, this could work for task related events
but will need to think about how to do this for cpu related events which hit the same issue and we dont have a task to flag.. maybe do it the same way as for TIF_SYSCALL_TRACEPOINT and flag everyone ;)
jirka
| |