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 v2 -> v3 -------------- * Redefined the event format for 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 | 319 +++++++++++++++++++++- arch/powerpc/platforms/powernv/opal-imc.c | 3 + include/linux/cpuhotplug.h | 1 + 5 files changed, 351 insertions(+), 12 deletions(-) -- 2.17.1