Messages in this thread | | | Date | Tue, 2 Oct 2012 18:16:47 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCHv2] perf x86_64: Fix rsp register for system call fast path |
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On Tue, Oct 02, 2012 at 06:06:26PM +0200, Jiri Olsa wrote: > On Tue, Oct 02, 2012 at 05:49:26PM +0200, Frederic Weisbecker wrote: > > On Tue, Oct 02, 2012 at 04:58:15PM +0200, Jiri Olsa wrote: > > > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > > > index 915b876..11d62ff 100644 > > > --- a/arch/x86/kernel/cpu/perf_event.c > > > +++ b/arch/x86/kernel/cpu/perf_event.c > > > @@ -34,6 +34,7 @@ > > > #include <asm/timer.h> > > > #include <asm/desc.h> > > > #include <asm/ldt.h> > > > +#include <asm/syscall.h> > > > > > > #include "perf_event.h" > > > > > > @@ -1699,6 +1700,52 @@ void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now) > > > userpg->time_offset = this_cpu_read(cyc2ns_offset) - now; > > > } > > > > > > +#ifdef CONFIG_X86_64 > > > +__weak int arch_sample_regs_user(struct pt_regs *oregs, struct pt_regs *regs) > > > +{ > > > + int kernel = !user_mode(regs); > > > + > > > + if (kernel) { > > > + if (current->mm) > > > + regs = task_pt_regs(current); > > > + else > > > + regs = NULL; > > > + } > > > > Shouldn't the above stay in generic code? > > could be.. I guess I thought that having the regs retrieval > plus the fixup at the same place feels better/compact ;) > > but could change that if needed
Yeah please.
> > > > I'm trying to scratch my head to find a solution to detect the race and > > bail out instead of recording erroneous values but I can't find one. > > > > Anyway this is still better than what we have now. > > > > Another solution could be to force syscall slow path and have some variable > > set there that tells us we are in a syscall and every regs have been saved. > > > > But we probably don't want to force syscall slow path... > > I was trying something like that as well, but the one I sent looks > far less hacky to me.. :)
Actually it's more hacky because it's less deterministic. But it's more simple, and doesn't hurt performances.
Ok, let's start with that.
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