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

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Date:   Wed, 15 Aug 2018 10:39:13 +0100
From:   Will Deacon <will.deacon@....com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Kim Phillips <kim.phillips@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>, ast@...nel.org,
        Greg KH <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, suzuki.poulosi@....com,
        linux-s390@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration

On Tue, Aug 14, 2018 at 01:42:27PM -0600, Mathieu Poirier wrote:
> On Tue, 14 Aug 2018 at 11:09, Kim Phillips <kim.phillips@....com> wrote:
> > 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.

For the record, I will continue to oppose PMU drivers that dump diagnostics
about user-controlled input into dmesg, but the coresight drivers are yours
so it's up to you and I won't get in the way!

Will