linux-kernel - Re: [PATCH 1/2] powerpc/vpa_pmu: Add interface to expose vpa counters via perf

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Message-ID: <9c18c4d4-ee60-4543-8bbb-ddc729c0a0f5@linux.ibm.com>
Date: Fri, 13 Sep 2024 14:05:26 +0530
From: kajoljain <kjain@...ux.ibm.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>, mpe@...erman.id.au
Cc: atrajeev@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, maddy@...ux.ibm.com,
        disgoel@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org,
        hbathini@...ux.ibm.com, adubey@...ux.ibm.com
Subject: Re: [PATCH 1/2] powerpc/vpa_pmu: Add interface to expose vpa counters
 via perf



On 9/13/24 12:00, Christophe Leroy wrote:
> 
> 
> Le 28/08/2024 à 12:21, Kajol Jain a écrit :
>> The pseries Shared Processor Logical Partition(SPLPAR) machines
>> can retrieve a log of dispatch and preempt events from the
>> hypervisor using data from Disptach Trace Log(DTL) buffer.
>> With this information, user can retrieve when and why each dispatch &
>> preempt has occurred. Added an interface to expose the Virtual Processor
>> Area(VPA) DTL counters via perf.
>>
>> The following events are available and exposed in sysfs:
>>
>>   vpa_dtl/dtl_cede/ - Trace voluntary (OS initiated) virtual processor
>> waits
>>   vpa_dtl/dtl_preempt/ - Trace time slice preempts
>>   vpa_dtl/dtl_fault/ - Trace virtual partition memory page faults.
>>   vpa_dtl/dtl_all/ - Trace all (dtl_cede/dtl_preempt/dtl_fault)
>>
>> Added interface defines supported event list, config fields for the
>> event attributes and their corresponding bit values which are exported
>> via sysfs. User could use the standard perf tool to access perf events
>> exposed via vpa-dtl pmu.
>>
>> The VPA DTL PMU counters do not interrupt on overflow or generate any
>> PMI interrupts. Therefore, the kernel needs to poll the counters, added
>> hrtimer code to do that. The timer interval can be provided by user via
>> sample_period field in nano seconds.
>>
>> Result on power10 SPLPAR system with 656 cpu threads.
>> In the below perf record command with vpa_dtl pmu, -c option is used
>> to provide sample_period whch corresponding to 1000000000ns i.e; 1sec
>> and the workload time is also 1 second, hence we are getting 656 samples:
>>
>> [command] perf record -a -R -e vpa_dtl/dtl_all/ -c 1000000000 sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.828 MB perf.data (656 samples) ]
>>
>> There is one hrtimer added per vpa-dtl pmu thread. Code added to handle
>> addition of dtl buffer data in the raw sample. Since DTL does not provide
>> IP address for a sample and it just have traces on reason of
>> dispatch/preempt, we directly saving DTL buffer data to perf.data file as
>> raw sample. For each hrtimer restart call, interface will dump all the
>> new dtl entries added to dtl buffer as a raw sample.
>>
>> To ensure there are no other conflicting dtl users (example: debugfs dtl
>> or /proc/powerpc/vcpudispatch_stats), interface added code to use
>> "down_write_trylock" call to take the dtl_access_lock. The
>> dtl_access_lock
>> is defined in dtl.h file. Also added global reference count variable
>> called
>> "dtl_global_refc", to ensure dtl data can be captured per-cpu. Code also
>> added global lock called "dtl_global_lock" to avoid race condition.
>>
>> Signed-off-by: Kajol Jain <kjain@...ux.ibm.com>
>> ---
>> Notes:
>>
>> - Made code changes on top of recent fix sent by Michael Ellerman.
>>    Link to the patch:
>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20240819122401.513203-1-mpe@ellerman.id.au/
>>
>>   arch/powerpc/perf/Makefile  |   2 +-
>>   arch/powerpc/perf/vpa-pmu.c | 469 ++++++++++++++++++++++++++++++++++++
>>   include/linux/cpuhotplug.h  |   1 +
>>   3 files changed, 471 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/powerpc/perf/vpa-pmu.c
> 
> 
> Seems like it doesn't build on PPC64:
> 
> arch/powerpc/perf/vpa-pmu.c#L212
> passing argument 1 of 'up_write' from incompatible pointer type
> [-Wincompatible-pointer-types]
> 
> arch/powerpc/perf/vpa-pmu.c#L261
> passing argument 1 of 'down_write_trylock' from incompatible pointer
> type [-Wincompatible-pointer-types]
> 
> arch/powerpc/perf/vpa-pmu.c#L402
> passing argument 1 of 'up_write' from incompatible pointer type
> [-Wincompatible-pointer-types]

Hi Christophe,
   Thanks for checking the patch. These changes are on top of fix patch
sent by Michael Ellerman
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20240819122401.513203-1-mpe@ellerman.id.au/

Since he changed the dtl_access_lock to be a rw_semaphore.

Are you trying with Michael patch changes?

Thanks,
Kajol Jain