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From: Peter Zijlstra <peterz@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: "kasong@redhat.com" <kasong@redhat.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: Getting empty callchain from perf_callchain_kernel()
Date: Fri, 17 May 2019 10:10:57 +0200	[thread overview]
Message-ID: <20190517081057.GQ2650@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190517074600.GJ2623@hirez.programming.kicks-ass.net>

On Fri, May 17, 2019 at 09:46:00AM +0200, Peter Zijlstra wrote:
> On Thu, May 16, 2019 at 11:51:55PM +0000, Song Liu wrote:
> > Hi, 
> > 
> > We found a failure with selftests/bpf/tests_prog in test_stacktrace_map (on bpf/master
> > branch). 
> > 
> > After digging into the code, we found that perf_callchain_kernel() is giving empty
> > callchain for tracepoint sched/sched_switch. And it seems related to commit
> > 
> > d15d356887e770c5f2dcf963b52c7cb510c9e42d
> > ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
> > 
> > Before this commit, perf_callchain_kernel() returns callchain with regs->ip. With
> > this commit, regs->ip is not sent for !perf_hw_regs(regs) case. 
> 
> So while I think the below is indeed right; we should store regs->ip
> regardless of the unwind path chosen, I still think there's something
> fishy if this results in just the 1 entry.
> 
> The sched/sched_switch event really should have a non-trivial stack.
> 
> Let me see if I can reproduce with just perf.

$ perf record -g -e "sched:sched_switch" -- make clean
$ perf report -D

12 904071759467 0x1790 [0xd0]: PERF_RECORD_SAMPLE(IP, 0x1): 7236/7236: 0xffffffff81c29562 period: 1 addr: 0
... FP chain: nr:10
.....  0: ffffffffffffff80
.....  1: ffffffff81c29562
.....  2: ffffffff81c29933
.....  3: ffffffff8111f688
.....  4: ffffffff81120b9d
.....  5: ffffffff81120ce5
.....  6: ffffffff8100254a
.....  7: ffffffff81e0007d
.....  8: fffffffffffffe00
.....  9: 00007f9b6cd9682a
... thread: sh:7236
...... dso: /lib/modules/5.1.0-12177-g41bbb9129767/build/vmlinux


IOW, it seems to 'work'.


  reply	other threads:[~2019-05-17  8:11 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16 23:51 Getting empty callchain from perf_callchain_kernel() Song Liu
2019-05-17  7:46 ` Peter Zijlstra
2019-05-17  8:10   ` Peter Zijlstra [this message]
2019-05-17  8:15     ` Kairui Song
2019-05-17  8:32       ` Kairui Song
2019-05-17 16:22         ` Song Liu
2019-05-17  9:10       ` Peter Zijlstra
2019-05-17 18:40         ` Song Liu
2019-05-17 21:06           ` Alexei Starovoitov
2019-05-17 21:48             ` Song Liu
2019-05-19 18:07               ` Kairui Song
2019-05-20 17:22                 ` Song Liu
2019-05-22 13:51                   ` Peter Zijlstra
2019-05-19 18:06         ` Kairui Song
2019-05-20 17:16           ` Song Liu
2019-05-20 17:19           ` Song Liu
2019-05-22 14:02           ` Peter Zijlstra
2019-05-22 14:49             ` Alexei Starovoitov
2019-05-22 17:45               ` Josh Poimboeuf
2019-05-22 23:46                 ` Josh Poimboeuf
2019-05-23  6:48                   ` Kairui Song
2019-05-23  8:27                     ` Song Liu
2019-05-23  9:11                       ` Kairui Song
2019-05-23 13:32                     ` Josh Poimboeuf
2019-05-23 14:50                       ` Kairui Song
2019-05-23 15:24                         ` Josh Poimboeuf
2019-05-23 16:41                           ` Kairui Song
2019-05-23 17:27                             ` Josh Poimboeuf
2019-05-24  2:20                               ` Kairui Song
2019-05-24 23:23                                 ` Josh Poimboeuf
2019-05-27 11:57                                   ` Kairui Song
2019-06-06 16:04                                     ` Song Liu
2019-06-06 23:58                                       ` Josh Poimboeuf
2019-06-11 21:03                                       ` Josh Poimboeuf
2019-05-24  8:53                           ` Peter Zijlstra
2019-05-24 13:05                             ` Josh Poimboeuf
2019-06-12  3:05                             ` Josh Poimboeuf
2019-06-12  8:54                               ` Peter Zijlstra
2019-06-12 14:50                                 ` Josh Poimboeuf
2019-06-13 20:26                                   ` Josh Poimboeuf
2019-06-12 13:10                               ` Steven Rostedt
2019-06-12 14:26                                 ` Josh Poimboeuf
2019-05-22 18:07       ` Josh Poimboeuf
2019-05-22 21:55         ` Alexei Starovoitov
2019-05-17 16:32     ` Song Liu

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