Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage!

From: Andi Kleen
Date: Tue Nov 22 2016 - 14:07:05 EST

On Tue, Nov 22, 2016 at 09:39:45AM -0500, Steven Rostedt wrote:
> On Mon, 21 Nov 2016 10:37:00 -0800
> Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> > Here is it again untruncated:
> >
> >
> BTW, what tool did you use to generate this?

perf and Intel PT, with the disassembler patches added and udis86

You need a CPU that supports PT, like Broadwell, Skylake, Goldmont.

# enable trace point
perf record -e intel_pt// -a sleep X
perf script --itrace=i0ns --ns -F cpu,ip,time,asm,sym

On Skylake can also get more accurate timing by enabling cycle timing
(at the cost of some overhead)

perf record -e intel_pt/cyc=1,cyc_thresh=1/ -a ...

The earlier trace didn't have that enabled.