Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration

From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: Kim Phillips <kim.phillips@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>, Jiri Olsa <jolsa@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	ast@kernel.org, Greg KH <gregkh@linuxfoundation.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	suzuki.poulosi@arm.com, linux-s390@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration
Date: Tue, 14 Aug 2018 13:42:27 -0600	[thread overview]
Message-ID: <CANLsYkxZ_Wts6k9yqJhJf_R5oh74svpcuoNxhtFf6h3mz8U4ZA@mail.gmail.com> (raw)
In-Reply-To: <20180814120910.ed225bbc462c58b09e5d68de@arm.com>

On Tue, 14 Aug 2018 at 11:09, Kim Phillips <kim.phillips@arm.com> wrote:
>
> On Tue, 14 Aug 2018 10:15:56 -0600
> Mathieu Poirier <mathieu.poirier@linaro.org> wrote:
>
> > On Mon, 13 Aug 2018 at 11:46, Kim Phillips <kim.phillips@arm.com> wrote:
> > > It yields success for the --per-thread case..:
> > >
> > > $ sudo taskset -c 0 ./perf record -e cs_etm/@20010000.etf/ --per-thread uname -a
> > > Linux juno 4.18.0-rc8-00011-gb82af52c4b35-dirty #147 SMP PREEMPT Thu Aug 9 11:20:37 CDT 2018 aarch64 GNU/Linux
> > > [ perf record: Woken up 0 times to write data ]
> > > Warning:
> > > AUX data lost 1 times out of 2!
> > >
> > > [ perf record: Captured and wrote 0.067 MB perf.data ]
> > > $
> > >
> > > ..but not for CPU-wide?:
> > >
> > > $ sudo taskset -c 0 ./perf record -e cs_etm/@20010000.etf/ uname -a
> > > failed to mmap with 12 (Cannot allocate memory)
> > > $ sudo taskset -c 0 ./perf record -e cs_etm/@20010000.etf/ -C 0 uname -a
> > > failed to mmap with 12 (Cannot allocate memory)
> > > $
> >
> > This patchset is getting very old and a fair amount of things have
> > changed since then.  I'm hoping to be coming out with a new one
> > shortly.  Nonetheless the above is returning an error in CPU-wide
> > scenarios while the feature is being implemented.  Isn't what you
> > requested or have I misunderstood your comment?
>
> No, sigh, I just automatically assumed the patchset would include
> CPU-wide support again.  If it were being done that way, we'd all know
> that the feature(s) this patchset adds would be doing the right thing
> for that purpose, guaranteed.

The patchset published on this list never had support for CPU-wide scenarios.

This is only a preparatory step, the first one in a few more to come.
Sending the whole thing in one go would be way too heavy and is not
realistic.

>
> The other thing that's going on here is that I'm becoming numb to the
> loathsome "failed to mmap with 12 (Cannot allocate memory)" being
> returned no matter what the error is/was. E.g., an error that would
> indicate a sense of non-implementation would be much better
> appreciated than presumably what the above is doing, i.e., returning
> -ENOMEM.  That, backed up with specific details in the form of human
> readable text in dmesg would be *most* welcome.

As part of the refactoring of the code to support CPU-wide scenarios I
intend to emit better diagnostic messages from the driver.  Modifying
rb_alloc_aux() to propagate the error message generated by the
architecture specific PMUs doesn't look hard either and I _may_ get to
it as part of this work.

Mathieu

>
> Thanks,
>
> Kim