Messages in this thread Patch in this message | | | Date | Fri, 29 Jun 2012 13:37:59 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC 09/23] x86_64: Store userspace rsp in system_call fastpath |
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On Fri, Jun 29, 2012 at 10:03:27AM +0200, Jiri Olsa wrote: > 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 ;)
You can also hook into tasks sched_in/out on cpu wide events. Just add something like:
diff --git a/kernel/events/core.c b/kernel/events/core.c index 5b06cbb..be8f18a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5987,7 +5987,8 @@ done: } if (!event->parent) { - if (event->attach_state & PERF_ATTACH_TASK) + if (event->attach_state & PERF_ATTACH_TASK || + event->attr.sample_type & PERF_SAMPLE_USER_REGS) static_key_slow_inc(&perf_sched_events.key); if (event->attr.mmap || event->attr.mmap_data) atomic_inc(&nr_mmap_events);
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