[Skiboot-stable] [PATCH v3 0/7] skiboot: OPAL support for IMC trace-mode
Anju T Sudhakar
anju at linux.vnet.ibm.com
Fri Mar 22 17:43:45 AEDT 2019
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 at 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.
----------------
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 v2 -> v3
-------------
* factored out the code for stop api in core and trace-imc opal-init.
* Added sufficient documentation for imc-trace mode.
Anju T Sudhakar (7):
doc/imc: Edit imc.rst documentation to include
doc/device-tree: Edit device tree documentation for imc to include
trace-node information.
doc/opal-api: Edit documentation for IMC opal call to include
trace-imc
include/imc: Trace IMC Macro definitions
hw/imc: Refactor opal init call for core-imc
hw/imc: Enable opal calls to init/start/stop IMC Trace mode
external/mambo: Mambo hack to add trace-imc nodes in the device-tree
doc/device-tree/imc.rst | 50 ++++++++++
doc/imc.rst | 67 +++++++++++++
doc/opal-api/opal-imc-counters.rst | 17 ++--
external/mambo/skiboot.tcl | 21 +++++
hw/imc.c | 146 +++++++++++++++++++++++------
include/imc.h | 30 ++++++
include/opal-api.h | 1 +
7 files changed, 296 insertions(+), 36 deletions(-)
--
2.17.2
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