Messages in this thread | | | Date | Fri, 29 Apr 2011 02:33:04 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 1/2] trace: Add trap entry/exit tracepoints |
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On Fri, 22 Apr 2011, Vaibhav Nagarnaik wrote: > #include <asm/uaccess.h> > #include <asm/pgtable.h> > #include <asm/system.h> > @@ -1330,8 +1332,10 @@ void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, > struct siginfo info; > > fill_sigtrap_info(tsk, regs, error_code, si_code, &info); > + trace_trap_entry(tsk->thread.trap_no);
What the heck? How is that a trap? The code is sending SIGTRAP not entering a trap at all. What are you trying to measure ? The time it takes to send SIGTRAP? So how is that useful as an extra event?
> /* Send us the fake SIGTRAP */ > force_sig_info(SIGTRAP, &info, tsk); > + trace_trap_exit(tsk->thread.trap_no); > } > > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index 4857ff6..d450349 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -33,6 +33,9 @@ > #include <linux/io.h> > #include <trace/events/irq.h> > > +#define CREATE_TRACE_POINTS > +#include <trace/events/trap.h> > + > #ifdef CONFIG_EISA > #include <linux/ioport.h> > #include <linux/eisa.h> > @@ -123,6 +126,7 @@ do_trap(int trapnr, int signr, char *str, struct pt_regs *regs, > { > struct task_struct *tsk = current; > > + trace_trap_entry(trapnr);
While the event of do_trap() itself might be interesting, it does not matter at all how long it takes to handle it. That code is really not so interesting.
> @@ -286,7 +293,9 @@ do_general_protection(struct pt_regs *regs, long error_code) > printk("\n"); > } > > + trace_trap_entry(tsk->thread.trap_no); > force_sig(SIGSEGV, tsk); > + trace_trap_exit(tsk->thread.trap_no);
We really do not care how long the force_sig() call takes. It's irrelevant. The only interesting thing here is that we ran into a GP trap.
> + > +dotraplinkage void __kprobes > +do_page_fault(struct pt_regs *regs, unsigned long error_code) > +{ > + trace_trap_entry(14);
Yuck. Magic number 14 ? Why not 42 ?
> + __do_page_fault(regs, error_code); > + trace_trap_exit(14); > +}
That page fault thing is the only interesting event in terms of runtime, but I have yet to see a proper rationale for the whole thing aside of that completly bogus changelog which tells what output I can produce, but not why the hell it is a good idea to add all that trace points.
Thanks,
tglx
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