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Date: Tue, 16 Apr 2019 15:14:49 +0530
From: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
To: mpe@...erman.id.au
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 0/5] powerpc/perf: IMC trace-mode support
Hi,
Kindly ignore this series, since patch 5/5 in this series doesn't
incorporate the event-format change
that I've done in v4 of this series.
Apologies for the inconvenience. I will post the updated v5 soon.
Thanks,
Anju
On 4/15/19 3:41 PM, Anju T Sudhakar wrote:
> IMC (In-Memory collection counters) is a hardware monitoring facility
> that collects large number of hardware performance events.
> POWER9 support two modes for IMC which are the Accumulation mode and
> Trace mode. In Accumulation mode, event counts are accumulated in system
> Memory. Hypervisor then reads the posted counts periodically or when
> requested. In IMC Trace mode, the 64 bit trace scom value is initialized
> with the event information. The CPMC*SEL and CPMC_LOAD in the trace scom, specifies
> the event to be monitored and the sampling duration. On each overflow in the
> CPMC*SEL, hardware snapshots the program counter along with event counts
> and writes into memory pointed by LDBAR. LDBAR has bits to indicate whether
> hardware is configured for accumulation or trace mode.
> Currently the event monitored for trace-mode is fixed as cycle.
>
> Trace-IMC Implementation:
> --------------------------
> To enable trace-imc, we need to
>
> * Add trace node in the DTS file for power9, so that the new trace node can
> be discovered by the kernel.
>
> Information included in the DTS file are as follows, (a snippet from
> the ima-catalog)
>
> TRACE_IMC: trace-events {
> #address-cells = <0x1>;
> #size-cells = <0x1>;
> event at 10200000 {
> event-name = "cycles" ;
> reg = <0x10200000 0x8>;
> desc = "Reference cycles" ;
> };
> };
> trace@0 {
> compatible = "ibm,imc-counters";
> events-prefix = "trace_";
> reg = <0x0 0x8>;
> events = < &TRACE_IMC >;
> type = <0x2>;
> size = <0x40000>;
> };
>
> OP-BUILD changes needed to include the "trace node" is already pulled in
> to the ima-catalog repo.
>
> ps://github.com/open-power/op-build/commit/d3e75dc26d1283d7d5eb444bff1ec9e40d5dfc07
>
> * Enchance the opal_imc_counters_* calls to support this new trace mode
> in imc. Add support to initialize the trace-mode scom.
>
> TRACE_IMC_SCOM bit representation:
>
> 0:1 : SAMPSEL
> 2:33 : CPMC_LOAD
> 34:40 : CPMC1SEL
> 41:47 : CPMC2SEL
> 48:50 : BUFFERSIZE
> 51:63 : RESERVED
>
> CPMC_LOAD contains the sampling duration. SAMPSEL and CPMC*SEL determines
> the event to count. BUFFRSIZE indicates the memory range. On each overflow,
> hardware snapshots program counter along with event counts and update the
> memory and reloads the CMPC_LOAD value for the next sampling duration.
> IMC hardware does not support exceptions, so it quietly wraps around if
> memory buffer reaches the end.
>
> OPAL support for IMC trace mode is already upstream.
>
> * Set LDBAR spr to enable imc-trace mode.
>
> LDBAR Layout:
>
> 0 : Enable/Disable
> 1 : 0 -> Accumulation Mode
> 1 -> Trace Mode
> 2:3 : Reserved
> 4-6 : PB scope
> 7 : Reserved
> 8:50 : Counter Address
> 51:63 : Reserved
>
> ----------------------
>
> PMI interrupt handling is avoided, since IMC trace mode snapshots the
> program counter and update to the memory. And this also provide a way for
> the operating system to do instruction sampling in real time without
> PMI(Performance Monitoring Interrupts) processing overhead.
> Performance data using 'perf top' with and without trace-imc event:
>
> PMI interrupts count when `perf top` command is executed without trace-imc event.
>
> # cat /proc/interrupts (a snippet from the output)
> 9944 1072 804 804 1644 804 1306
> 804 804 804 804 804 804 804
> 804 804 1961 1602 804 804 1258
> [-----------------------------------------------------------------]
> 803 803 803 803 803 803 803
> 803 803 803 803 804 804 804
> 804 804 804 804 804 804 803
> 803 803 803 803 803 1306 803
> 803 Performance monitoring interrupts
>
>
> `perf top` with trace-imc (executed right after 'perf top' without trace-imc event):
>
> # perf top -e trace_imc/trace_cycles/
> 12.50% [kernel] [k] arch_cpu_idle
> 11.81% [kernel] [k] __next_timer_interrupt
> 11.22% [kernel] [k] rcu_idle_enter
> 10.25% [kernel] [k] find_next_bit
> 7.91% [kernel] [k] do_idle
> 7.69% [kernel] [k] rcu_dynticks_eqs_exit
> 5.20% [kernel] [k] tick_nohz_idle_stop_tick
> [-----------------------]
>
> # cat /proc/interrupts (a snippet from the output)
>
> 9944 1072 804 804 1644 804 1306
> 804 804 804 804 804 804 804
> 804 804 1961 1602 804 804 1258
> [-----------------------------------------------------------------]
> 803 803 803 803 803 803 803
> 803 803 803 804 804 804 804
> 804 804 804 804 804 804 803
> 803 803 803 803 803 1306 803
> 803 Performance monitoring interrupts
>
> The PMI interrupts count remains the same.
>
>
> Changelog:
> ----------
> From v3 -> v4:
>
> * trace_imc_refc is introduced. So that even if, core-imc
> is disabled, trace-imc can be used.
>
> * trace_imc_pmu_sched_task is removed and opal start/stop
> is invoked in trace_imc_event_add/del function.
>
>
> Suggestions/comments are welcome.
>
> Anju T Sudhakar (4):
> powerpc/include: Add data structures and macros for IMC trace mode
> powerpc/perf: Rearrange setting of ldbar for thread-imc
> powerpc/perf: Trace imc events detection and cpuhotplug
> powerpc/perf: Trace imc PMU functions
>
> Madhavan Srinivasan (1):
> powerpc/perf: Add privileged access check for thread_imc
>
> arch/powerpc/include/asm/imc-pmu.h | 39 +++
> arch/powerpc/include/asm/opal-api.h | 1 +
> arch/powerpc/perf/imc-pmu.c | 318 +++++++++++++++++++++-
> arch/powerpc/platforms/powernv/opal-imc.c | 3 +
> include/linux/cpuhotplug.h | 1 +
> 5 files changed, 351 insertions(+), 11 deletions(-)
>
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