Re: [PATCH v3 0/7] MIPS: perf: MT fixes and improvements

[Florian Fainelli]

On 04/20/2018 03:23 AM, Matt Redfearn wrote:
> This series addresses a few issues with how the MIPS performance
> counters code supports the hardware multithreading MT ASE.
> 
> Firstly, implementations of the MT ASE may implement performance
> counters
> per core or per thread(TC). MIPS Techologies implementations signal this
> via a bit in the implmentation specific CONFIG7 register. Since this
> register is implementation specific, checking it should be guarded by a
> PRID check. This also replaces a bit defined by a magic number.
> 
> Secondly, the code currently uses vpe_id(), defined as
> smp_processor_id(), divided by 2, to share core performance counters
> between VPEs. This relies on a couple of assumptions of the hardware
> implementation to function correctly (always 2 VPEs per core, and the
> hardware reading only the least significant bit).
> 
> Finally, the method of sharing core performance counters between VPEs is
> suboptimal since it does not allow one process running on a VPE to use
> all of the performance counters available to it, because the kernel will
> reserve half of the coutners for the other VPE even if it may never use
> them. This reservation at counter probe is replaced with an allocation
> on use strategy.
> 
> Tested on a MIPS Creator CI40 (2C2T MIPS InterAptiv with per-TC
> counters, though for the purposes of testing the per-TC availability was
> hardcoded to allow testing both paths).
> 
> Series applies to v4.16

Sorry it took so long to get that tested.

Sounds like you need to build test this on a BMIPS5000 configuration
(bmips_stb_defconfig should provide that):

In file included from ./arch/mips/include/asm/mach-generic/spaces.h:15:0,
                 from ./arch/mips/include/asm/mach-bmips/spaces.h:16,
                 from ./arch/mips/include/asm/addrspace.h:13,
                 from ./arch/mips/include/asm/barrier.h:11,
                 from ./include/linux/compiler.h:245,
                 from ./include/linux/kernel.h:10,
                 from ./include/linux/cpumask.h:10,
                 from arch/mips/kernel/perf_event_mipsxx.c:18:
arch/mips/kernel/perf_event_mipsxx.c: In function 'mipsxx_pmu_enable_event':
./arch/mips/include/asm/mipsregs.h:738:52: error: suggest parentheses
around '+' in operand of '&' [-Werror=parentheses]
 #define BRCM_PERFCTRL_VPEID(v) (_ULCAST_(1) << (12 + v))

arch/mips/kernel/perf_event_mipsxx.c:385:10: note: in expansion of macro
'BRCM_PERFCTRL_VPEID'
   ctrl = BRCM_PERFCTRL_VPEID(cpu & MIPS_CPUID_TO_COUNTER_MASK);
          ^~~~~~~~~~~~~~~~~~~
  CC      drivers/of/fdt_addres

after fixing that, I tried the following to see whether this would be a
good test case to exercise against:

perf record -a -C 0 taskset -c 1 /bin/true
perf record -a -C 1 taskset -c 0 /bin/true

and would not see anything related to /bin/true running in either case,
which seems like it does the right thing?

Tested-by: Florian Fainelli <f.fainelli@xxxxxxxxx>

BTW, for some reason not specifying -a -C <cpu> does lead to lockups,
consistently and for pretty much any perf command, this could be BMIPS
specific, did not get a chance to cross test on a different machine.

> 
> 
> Changes in v3:
> New patch to detect feature presence in cpu-probe.c
> Use flag in cpu_data set by cpu_probe.c to indicate feature presence.
> - rebase on new feature detection
> 
> Changes in v2:
> Fix mipsxx_pmu_enable_event for !#ifdef CONFIG_MIPS_MT_SMP
> - Fix !#ifdef CONFIG_MIPS_PERF_SHARED_TC_COUNTERS build
> - re-use cpuc variable in mipsxx_pmu_alloc_counter,
>   mipsxx_pmu_free_counter rather than having sibling_ version.
> Since BMIPS5000 does not implement per TC counters, we can remove the
> check on cpu_has_mipsmt_pertccounters.
> New patch to fix BMIPS5000 system mode perf.
> 
> Matt Redfearn (7):
>   MIPS: Probe for MIPS MT perf counters per TC
>   MIPS: perf: More robustly probe for the presence of per-tc counters
>   MIPS: perf: Use correct VPE ID when setting up VPE tracing
>   MIPS: perf: Fix perf with MT counting other threads
>   MIPS: perf: Allocate per-core counters on demand
>   MIPS: perf: Fold vpe_id() macro into it's one last usage
>   MIPS: perf: Fix BMIPS5000 system mode counting
> 
>  arch/mips/include/asm/cpu-features.h |   7 ++
>  arch/mips/include/asm/cpu.h          |   2 +
>  arch/mips/include/asm/mipsregs.h     |   6 +
>  arch/mips/kernel/cpu-probe.c         |  12 ++
>  arch/mips/kernel/perf_event_mipsxx.c | 232 +++++++++++++++++++----------------
>  arch/mips/oprofile/op_model_mipsxx.c |   2 -
>  6 files changed, 150 insertions(+), 111 deletions(-)
> 


-- 
Florian