Messages in this thread Patch in this message | | | Date | Tue, 12 May 2020 23:01:03 +0200 | From | Thomas Gleixner <> | Subject | [patch V5 04/38] x86: Make hardware latency tracing explicit |
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The hardware latency tracer calls into trace_sched_clock and ends up in various instrumentable functions which is problemeatic vs. the kprobe handling especially the text poke machinery. It's invoked from nmi_enter/exit(), i.e. non-instrumentable code.
Use nmi_enter/exit_notrace() instead. These variants do not invoke the hardware latency tracer which avoids chasing down complex callchains to make them non-instrumentable.
The real interesting measurement is the actual NMI handler. Add an explicit invocation for the hardware latency tracer to it.
#DB and #BP are uninteresting as they really should not be in use when analzying hardware induced latencies.
If #DF hits, hardware latency is definitely not interesting anymore and in case of a machine check the hardware latency is not the most troublesome issue either.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- V5: New patch --- arch/x86/kernel/cpu/mce/core.c | 4 ++-- arch/x86/kernel/nmi.c | 6 ++++-- arch/x86/kernel/traps.c | 10 +++++----- 3 files changed, 11 insertions(+), 9 deletions(-)
--- a/arch/x86/kernel/cpu/mce/core.c +++ b/arch/x86/kernel/cpu/mce/core.c @@ -1916,7 +1916,7 @@ static __always_inline void exc_machine_ mce_check_crashing_cpu()) return; - nmi_enter(); + nmi_enter_notrace(); /* * The call targets are marked noinstr, but objtool can't figure * that out because it's an indirect call. Annotate it. @@ -1924,7 +1924,7 @@ static __always_inline void exc_machine_ instrumentation_begin(); machine_check_vector(regs); instrumentation_end(); - nmi_exit(); + nmi_exit_notrace(); } static __always_inline void exc_machine_check_user(struct pt_regs *regs) --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -334,6 +334,7 @@ static noinstr void default_do_nmi(struc __this_cpu_write(last_nmi_rip, regs->ip); instrumentation_begin(); + ftrace_nmi_enter(); handled = nmi_handle(NMI_LOCAL, regs); __this_cpu_add(nmi_stats.normal, handled); @@ -420,6 +421,7 @@ static noinstr void default_do_nmi(struc unknown_nmi_error(reason, regs); out: + ftrace_nmi_exit(); instrumentation_end(); } @@ -536,14 +538,14 @@ DEFINE_IDTENTRY_NMI(exc_nmi) } #endif - nmi_enter(); + nmi_enter_notrace(); inc_irq_stat(__nmi_count); if (!ignore_nmis) default_do_nmi(regs); - nmi_exit(); + nmi_exit_notrace(); #ifdef CONFIG_X86_64 if (unlikely(this_cpu_read(update_debug_stack))) { --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -378,7 +378,7 @@ DEFINE_IDTENTRY_DF(exc_double_fault) } #endif - nmi_enter(); + nmi_enter_notrace(); instrumentation_begin(); notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV); @@ -624,11 +624,11 @@ DEFINE_IDTENTRY_RAW(exc_int3) instrumentation_end(); idtentry_exit(regs); } else { - nmi_enter(); + nmi_enter_notrace(); instrumentation_begin(); do_int3(regs); instrumentation_end(); - nmi_exit(); + nmi_exit_notrace(); } } @@ -827,7 +827,7 @@ static void noinstr handle_debug(struct static __always_inline void exc_debug_kernel(struct pt_regs *regs, unsigned long dr6) { - nmi_enter(); + nmi_enter_notrace(); /* * The SDM says "The processor clears the BTF flag when it * generates a debug exception." Clear TIF_BLOCKSTEP to keep @@ -849,7 +849,7 @@ static __always_inline void exc_debug_ke if (dr6) handle_debug(regs, dr6, false); - nmi_exit(); + nmi_exit_notrace(); } static __always_inline void exc_debug_user(struct pt_regs *regs,
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