Re: Problems with -b, and confusing error messages

[Venkat <vcheru@gmail.com>]

Hi Jonas,

What does "dmesg|grep PEBS" return? and is that any different with prior
kernel ?(could verify old dmesg outputs)

Thanks,
Venkat

On Wed, 2016-10-05 at 14:24 +0200, Jonas Wagner wrote:
> Hi,
> 
> Thanks a lot Arnaldo for your help!
> 
> Unfortunately the problem persists, even with generous permissions and
> when running as root :( Here are some more examples:
> 
> ---
> 
> jowagner@kirk3[~] % sudo perf record -b /bin/true
> Error: 'precise' request may not be supported. Try removing 'p' modifier.
> 
> jowagner@kirk3[~] % sudo perf record -b -e cycles /bin/true
> Error: No hardware sampling interrupt available.
> No APIC? If so then you can boot the kernel with the "lapic" boot
> parameter to force-enable it.
> 
> jowagner@kirk3[~] % perf evlist -v
> zero-sized file (perf.data), nothing to do!
> 
> jowagner@kirk3[~] % sudo perf record /bin/true
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.014 MB perf.data (9 samples) ]
> 
> jowagner@kirk3[~] % perf evlist -v
> cycles:pp: size: 112, { sample_period, sample_freq }: 4000,
> sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1,
> comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 2,
> sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1
> 
> ---
> 
> Here are my settings in /proc/sys/kernel:
> /proc/sys/kernel/perf_cpu_time_max_percent         25
> /proc/sys/kernel/perf_event_max_sample_rate        100000
> /proc/sys/kernel/perf_event_mlock_kb               516
> /proc/sys/kernel/perf_event_paranoid               0
> /proc/sys/kernel/kptr_restrict                     0
> 
> And these are the CPU flags:
> model name      : Intel(R) Xeon(R) CPU E5-2697 v3 @ 2.60GHz
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
> syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts
> rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq
> dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm
> pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer xsave
> avx f16c rdrand lahf_lm abm epb tpr_shadow vnmi flexpriority ept vpid
> fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm xsaveopt
> cqm_llc cqm_occup_llc dtherm ida arat pln pts
> 
> Any other idea about the problem, or hints as to how I could debug it?
> 
> Best,
> Jonas
> 
> On Wed, Oct 5, 2016 at 1:11 PM, Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
> > Em Tue, Oct 04, 2016 at 05:02:58PM +0200, Jonas Wagner escreveu:
> >> I would like to ask for help, because perf stopped working when I
> >> enable taken branch stack sampling (with the -b option). Here are a
> >> few examples:
> >>
> >> $ perf record -b /bin/true
> >> Error:
> >> 'precise' request may not be supported. Try removing 'p' modifier.
> >>
> >> $ perf record -b -e cycles /bin/true
> >> Error:
> >> No hardware sampling interrupt available.
> >> No APIC? If so then you can boot the kernel with the "lapic" boot
> >> parameter to force-enable it.
> >>
> >> $ perf record -e cycles /bin/true
> >> [ perf record: Woken up 1 times to write data ]
> >> [ perf record: Captured and wrote 0.014 MB perf.data (8 samples) ]
> >>
> >> $ perf record -e cycles:p /bin/true
> >> [ perf record: Woken up 1 times to write data ]
> >> [ perf record: Captured and wrote 0.014 MB perf.data (9 samples) ]
> >>
> >> $ cat /proc/cmdline
> >> BOOT_IMAGE=/boot/vmlinuz-4.4.0-38-generic
> >> root=UUID=a5440a73-d559-4b61-808c-2430cd67ba25 ro quiet lapic
> >>
> >> I have a couple questions about this:
> >>
> >> 1. What's wrong? Branch stack sampling used to work on this machine...
> >> how can I make it work again?
> >> 2. Apparently, the problem is not related to the precise modifier, or
> >> the lapic boot parameter. Could we make these error messages more
> >> meaningful?
> >>
> >> Note regarding (1): I recently upgraded the kernel on this machine
> >> from 4.4.0-36-generic to 4.4.0-38-generic, on Ubuntu Xenial. Using the
> >> previous kernel, perf worked fine. It's tricky for me to undo the
> >> update though :(
> >>
> >> Help would be appreciated. Happy to provide more logs if needed. Thanks!
> >
> > So the message needs to be improved, no question about it, but can you
> > try running as root or tweaking perf_event_paranoid, as here I have:
> >
> > [root@jouet ~]# perf record -b /bin/true
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.024 MB perf.data (9 samples) ]
> > [root@jouet ~]# uname -a
> > Linux jouet 4.7.3-200.fc24.x86_64 #1 SMP Wed Sep 7 17:31:21 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
> > [root@jouet ~]# perf record -b /bin/true
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.024 MB perf.data (8 samples) ]
> > [root@jouet ~]# perf evlist -v
> > cycles:ppp: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD|BRANCH_STACK, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, branch_sample_type: ANY
> > [root@jouet ~]#
> >
> >
> > And, as user:
> >
> > [acme@jouet linux]$ perf record -b /bin/true
> > Error:
> > You may not have permission to collect stats.
> >
> > Consider tweaking /proc/sys/kernel/perf_event_paranoid,
> > which controls use of the performance events system by
> > unprivileged users (without CAP_SYS_ADMIN).
> >
> > The current value is 2:
> >
> >   -1: Allow use of (almost) all events by all users
> >>= 0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
> >>= 1: Disallow CPU event access by users without CAP_SYS_ADMIN
> >>= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN
> > [acme@jouet linux]$
> >
> > If I tweak /proc/sys/kernel/perf_event_paranoid, changing it from 2 to 1, say:
> >
> > [acme@jouet linux]$ perf record -b /bin/true
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.024 MB perf.data (9 samples) ]
> > [acme@jouet linux]$ perf evlist -v
> > cycles:ppp: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD|BRANCH_STACK, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, branch_sample_type: ANY
> > [acme@jouet linux]$
> >
> > It seems to work.
> >
> > IIRC there was a change in the default of /proc/sys/kernel/perf_event_paranoid
> > in Ubuntu recently, I bet this is the case.
> >
> > Probably they did that but forgot to update the tool, that would get better
> > error messages, but still not that good wrt branch stack support :-\
> >
> > - Arnaldo
> > --
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