Re: [PATCH] perf, x86: Optimize intel_pmu_pebs_fixup_ip()

[Don Zickus]

On Wed, Oct 16, 2013 at 03:31:25PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 16, 2013 at 08:46:49AM -0400, Don Zickus wrote:
> > On Wed, Oct 16, 2013 at 12:57:55PM +0200, Peter Zijlstra wrote:
> > > A prettier patch below. The main difference is on-demand allocation of
> > > the scratch buffer.
> > 
> > I'll see if I can sanity test this in the next couple hours.
> > 
> > Further testing yesterday showed that intel_pmu_drain_pebs_nhm still
> > has long latencies somewhere.  With 15 minute reboots, isolation goes
> > slooow.
> 
> Pick a smaller box? I seem to be able to reproduce on my wsm-ep, which
> boots inside a minute :-)

Heh.  It seemed to take longer on those boxes, but maybe I wasn't pushing
it hard enough. :-)

> 
> root@westmere:~# cd /debug/tracing/
> root@westmere:/debug/tracing# echo function > current_tracer
> root@westmere:/debug/tracing# cat available_filter_functions | grep ^inat > set_ftrace_notrace
> root@westmere:/debug/tracing# cat available_filter_functions | grep ^insn | grep -v get_length >> set_ftrace_notrace
> 

I guess now is a good time to learn ftrace.  Seems powerful if you know
how to use awk/sed/grep properly :-)

Thanks!  This might make debugging easier.

Cheers,
Don

> Run: perf top --stdio -e 'cycles:pp' in another window and when the
> console output shows:
> 
> [  610.319486] perf samples too long (19310 > 19230), lowering kernel.perf_event_max_sample_rate to 7000
> 
> quickly press enter here:
> 
> root@westmere:/debug/tracing# echo 0 > tracing_on
> root@westmere:/debug/tracing# cat trace > ~/trace1
> root@westmere:/debug/tracing# cat ~/trace1 | awk '/rcu_nmi_enter/ {
> t=gensub(":", "", "g", $4); cpu=gensub("[][]", "", "g", $2);
> start[cpu]=t; } /rcu_nmi_exit/ { x=gensub(":", "", "g", $4);
> cpu=gensub("[][]", "", "g", $2); t=start[cpu]; printf "%6.6f -- starting
> at: %6.6f on cpu: %d\n", x-t, t, cpu } ' | sort -n | tail -10
> 0.000037 -- starting at: 605.317795 on cpu: 9
> 0.000039 -- starting at: 602.831019 on cpu: 23
> 0.000039 -- starting at: 602.831148 on cpu: 6
> 0.000039 -- starting at: 602.955953 on cpu: 20
> 0.000040 -- starting at: 602.834012 on cpu: 18
> 0.000040 -- starting at: 602.956972 on cpu: 21
> 0.000040 -- starting at: 602.960048 on cpu: 22
> 0.000040 -- starting at: 609.290776 on cpu: 7
> 0.000075 -- starting at: 609.773875 on cpu: 0
> 0.009398 -- starting at: 610.319445 on cpu: 1
> root@westmere:/debug/tracing# grep "\[001\]" ~/trace1 | awk 'BEGIN {p=0}
> /610.319445/ {p=1} /rcu_nmi_exit/ {p=0} {if (p) print $0}'
> 
> Now obviously the whole printk stuff below is insane, but it does show
> its one that triggered the check. And the trace does give a fair idea of
> what its doing:
> 
>           <idle>-0     [001] d.h.   610.319445: rcu_nmi_enter <-do_nmi
>           <idle>-0     [001] d.h.   610.319446: nmi_handle.isra.3 <-do_nmi
>           <idle>-0     [001] d.h.   610.319447: intel_pmu_handle_irq <-perf_event_nmi_handler
>           <idle>-0     [001] d.h.   610.319447: intel_pmu_disable_all <-intel_pmu_handle_irq
>           <idle>-0     [001] d.h.   610.319448: intel_pmu_pebs_disable_all <-intel_pmu_disable_all
>           <idle>-0     [001] d.h.   610.319448: intel_pmu_lbr_disable_all <-intel_pmu_disable_all
>           <idle>-0     [001] d.h.   610.319449: intel_pmu_drain_bts_buffer <-intel_pmu_handle_irq
>           <idle>-0     [001] d.h.   610.319449: intel_pmu_lbr_read <-intel_pmu_handle_irq
>           <idle>-0     [001] d.h.   610.319453: intel_pmu_drain_pebs_nhm <-intel_pmu_handle_irq
>           <idle>-0     [001] d.h.   610.319453: __intel_pmu_pebs_event <-intel_pmu_drain_pebs_nhm
>           <idle>-0     [001] d.h.   610.319454: intel_pmu_save_and_restart <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319455: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319456: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319457: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319458: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319458: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319459: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319459: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319460: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319460: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319461: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319461: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319462: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319462: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319463: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319464: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319464: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319465: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319465: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319466: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319466: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319467: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319467: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319468: insn_get_length <-__intel_pmu_pebs_event
>           <idle>-0     [001] d.h.   610.319469: task_tgid_nr_ns <-perf_event_pid
>           <idle>-0     [001] d.h.   610.319469: __task_pid_nr_ns <-perf_event_tid
>           <idle>-0     [001] d.h.   610.319470: perf_output_begin <-perf_log_throttle
>           <idle>-0     [001] d.h.   610.319470: perf_output_copy <-perf_log_throttle
>           <idle>-0     [001] d.h.   610.319470: perf_output_copy <-perf_event__output_id_sample
>           <idle>-0     [001] d.h.   610.319471: perf_output_copy <-perf_event__output_id_sample
>           <idle>-0     [001] d.h.   610.319472: perf_output_copy <-perf_event__output_id_sample
>           <idle>-0     [001] d.h.   610.319472: perf_output_end <-perf_log_throttle
>           <idle>-0     [001] d.h.   610.319472: perf_output_put_handle <-perf_output_end
>           <idle>-0     [001] d.h.   610.319473: kvm_is_in_guest <-perf_misc_flags
>           <idle>-0     [001] d.h.   610.319473: task_tgid_nr_ns <-perf_event_pid
>           <idle>-0     [001] d.h.   610.319474: __task_pid_nr_ns <-perf_event_tid
>           <idle>-0     [001] d.h.   610.319474: kvm_is_in_guest <-perf_instruction_pointer
>           <idle>-0     [001] d.h.   610.319475: perf_output_begin <-__perf_event_overflow
>           <idle>-0     [001] d.h.   610.319475: perf_output_copy <-perf_output_sample
>           <idle>-0     [001] d.h.   610.319475: perf_output_copy <-perf_output_sample
>           <idle>-0     [001] d.h.   610.319476: perf_output_copy <-perf_output_sample
>           <idle>-0     [001] d.h.   610.319476: perf_output_copy <-perf_output_sample
>           <idle>-0     [001] d.h.   610.319476: perf_output_copy <-perf_output_sample
>           <idle>-0     [001] d.h.   610.319477: perf_output_copy <-perf_output_sample
>           <idle>-0     [001] d.h.   610.319477: perf_output_end <-__perf_event_overflow
>           <idle>-0     [001] d.h.   610.319477: perf_output_put_handle <-perf_output_end
>           <idle>-0     [001] d.h.   610.319478: intel_pmu_disable_event <-x86_pmu_stop
>           <idle>-0     [001] d.h.   610.319478: intel_pmu_lbr_disable <-intel_pmu_disable_event
>           <idle>-0     [001] d.h.   610.319479: intel_pmu_pebs_disable <-intel_pmu_disable_event
>           <idle>-0     [001] d.h.   610.319480: intel_pmu_enable_all <-intel_pmu_handle_irq
>           <idle>-0     [001] d.h.   610.319480: intel_pmu_pebs_enable_all <-intel_pmu_enable_all
>           <idle>-0     [001] d.h.   610.319480: intel_pmu_lbr_enable_all <-intel_pmu_enable_all
>           <idle>-0     [001] d.h.   610.319481: _raw_spin_trylock <-___ratelimit
>           <idle>-0     [001] d.h.   610.319482: _raw_spin_unlock_irqrestore <-___ratelimit
>           <idle>-0     [001] d.h.   610.319482: printk <-perf_sample_event_took
>           <idle>-0     [001] d.h.   610.319482: vprintk_emit <-printk
> 
> < snip ~8000 lines >
> 
>           <idle>-0     [001] d.h.   610.328841: wake_up_klogd <-console_unlock
>           <idle>-0     [001] d.h.   610.328841: arch_irq_work_raise <-irq_work_queue
>           <idle>-0     [001] d.h.   610.328842: apic_send_IPI_self <-arch_irq_work_raise
>           <idle>-0     [001] d.h.   610.328842: native_apic_wait_icr_idle <-arch_irq_work_raise
>           <idle>-0     [001] d.h.   610.328843: arch_trigger_all_cpu_backtrace_handler <-nmi_handle.isra.3
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