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

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Message-ID: <56b53876-0838-416f-adce-b1ffbd0916fc@csgroup.eu>
Date: Fri, 13 Sep 2024 08:30:41 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Kajol Jain <kjain@...ux.ibm.com>, 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



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]