[lkml]   [2020]   [Mar]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [patch 4/8] x86/entry: Move irq tracing on syscall entry to C-code
On Sun, Mar 1, 2020 at 7:21 AM Thomas Gleixner <> wrote:
> Andy Lutomirski <> writes:
> >> On Mar 1, 2020, at 2:16 AM, Thomas Gleixner <> wrote:
> >> Ok, but for the time being anything before/after CONTEXT_KERNEL is unsafe
> >> except trace_hardirq_off/on() as those trace functions do not allow to
> >> attach anything AFAICT.
> >
> > Can you point to whatever makes those particular functions special? I
> > failed to follow the macro maze.
> Those are not tracepoints and not going through the macro maze. See
> kernel/trace/trace_preemptirq.c

That has:

void trace_hardirqs_on(void)
if (this_cpu_read(tracing_irq_cpu)) {
if (!in_nmi())
trace_irq_enable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
this_cpu_write(tracing_irq_cpu, 0);


But this calls trace_irq_enable_rcuidle(), and that's the part of the
macro maze I got lost in. I found:

DEFINE_EVENT(preemptirq_template, irq_disable,
TP_PROTO(unsigned long ip, unsigned long parent_ip),
TP_ARGS(ip, parent_ip));

DEFINE_EVENT(preemptirq_template, irq_enable,
TP_PROTO(unsigned long ip, unsigned long parent_ip),
TP_ARGS(ip, parent_ip));
#define trace_irq_enable(...)
#define trace_irq_disable(...)
#define trace_irq_enable_rcuidle(...)
#define trace_irq_disable_rcuidle(...)

But the DEFINE_EVENT doesn't have the "_rcuidle" part. And that's
where I got lost in the macro maze. I looked at the gcc asm output,
and there is, indeed:

# ./include/trace/events/preemptirq.h:40:
DEFINE_EVENT(preemptirq_template, irq_enable,

with a bunch of asm magic that looks like it's probably a tracepoint.
I still don't quite see where the "_rcuidle" went.

But I also don't see why this is any different from any other tracepoint.


 \ /
  Last update: 2020-03-01 17:00    [W:0.083 / U:11.408 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site