[PATCH v2 0/5] powerpc/perf: IMC trace-mode support
From: Anju T Sudhakar
Date: Fri Dec 14 2018 - 04:11:32 EST
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, event counted is fixed for cycles and on
each overflow, hardware snapshots the program counter along with other
details and writes into memory pointed by LDBAR(ring buffer memory,
hardware wraps around). LDBAR has bit which indicates the IMC trace-mode.
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@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 other details 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.
Link to the skiboot patches to enhance the opal_imc_counters_* calls:
https://lists.ozlabs.org/pipermail/skiboot/2018-December/012878.html
https://lists.ozlabs.org/pipermail/skiboot/2018-December/012879.html
https://lists.ozlabs.org/pipermail/skiboot/2018-December/012882.html
https://lists.ozlabs.org/pipermail/skiboot/2018-December/012880.html
https://lists.ozlabs.org/pipermail/skiboot/2018-December/012881.html
https://lists.ozlabs.org/pipermail/skiboot/2018-December/012883.html
* 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
----------------
Key benefit of imc trace-mode is, each sample record contains the address
pointer along with other information. So that, we can profile the IP
without interrupting the application.
Performance data using 'perf top' with and without trace-imc event:
When the application is monitored with trace-imc event, we dont take any
PMI interrupts.
PMI interrupts count when `perf top` command is executed without trac-imc event.
# perf top
12.53% [kernel] [k] arch_cpu_idle
11.32% [kernel] [k] rcu_idle_enter
10.76% [kernel] [k] __next_timer_interrupt
9.49% [kernel] [k] find_next_bit
8.06% [kernel] [k] rcu_dynticks_eqs_exit
7.82% [kernel] [k] do_idle
5.71% [kernel] [k] tick_nohz_idle_stop_tic
[-----------------------]
# 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 (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 v1 -> v2
--------------
* Added privileged access check for thread-imc and trace-imc
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 | 297 +++++++++++++++++++++-
arch/powerpc/platforms/powernv/opal-imc.c | 3 +
include/linux/cpuhotplug.h | 1 +
5 files changed, 330 insertions(+), 11 deletions(-)
--
2.17.1