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Date: Fri, 27 Apr 2018 17:09:14 +0100 From: Will Deacon <will.deacon@....com> To: Kim Phillips <kim.phillips@....com> Cc: Mark Rutland <mark.rutland@....com>, Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, jnair@...iumnetworks.com, Robert.Richter@...ium.com, Vadim.Lomovtsev@...ium.com, Jan.Glauber@...ium.com, gklkml16@...il.com Subject: Re: [PATCH v4 2/2] ThunderX2: Add Cavium ThunderX2 SoC UNCORE PMU driver Kim, [Ganapat: please don't let this discussion disrupt your PMU driver development. You can safely ignore it for now :)] On Fri, Apr 27, 2018 at 10:46:29AM -0500, Kim Phillips wrote: > On Fri, 27 Apr 2018 15:37:20 +0100 > Will Deacon <will.deacon@....com> wrote: > > > On Fri, Apr 27, 2018 at 08:15:25AM -0500, Kim Phillips wrote: > > > On Fri, 27 Apr 2018 10:30:27 +0100 > > > Mark Rutland <mark.rutland@....com> wrote: > > > > On Thu, Apr 26, 2018 at 05:06:24PM -0500, Kim Phillips wrote: > > > > > On Wed, 25 Apr 2018 14:30:47 +0530 > > > > > Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com> wrote: > > > > > > > > > > > +static int thunderx2_uncore_event_init(struct perf_event *event) > > > > > > > > > This PMU driver can be made more user-friendly by not just silently > > > > > returning an error code such as -EINVAL, but by emitting a useful > > > > > message describing the specific error via dmesg. > > > > > > > > As has previously been discussed on several occasions, patches which log > > > > to dmesg in a pmu::event_init() path at any level above pr_debug() are > > > > not acceptable -- dmesg is not intended as a mechanism to inform users > > > > of driver-specific constraints. > > > > > > I disagree - drivers do it all the time, using dev_err(), dev_warn(), etc. > > > > > > > I would appreciate if in future you could qualify your suggestion with > > > > the requirement that pr_debug() is used. > > > > > > It shouldn't - the driver isn't being debugged, it's in regular use. > > > > For anything under drivers/perf/, I'd prefer not to have these prints > > and instead see efforts to improve error reporting via the perf system > > call interface. > > We'd all prefer that, and for all PMU drivers, why should ones under > drivers/perf be treated differently? Because they're the ones I maintain... > As you are already aware, I've personally tried to fix this problem - > that has existed since before the introduction of the perf tool (I > consider it a syscall-independent enhanced error interface), multiple > times, and failed. Why is that my problem? Try harder? > So until someone comes up with a solution that works for everyone > up to and including Linus Torvalds (who hasn't put up a problem > pulling PMU drivers emitting things to dmesg so far, by the way), this > keep PMU drivers' errors silent preference of yours is unnecessarily > impeding people trying to measure system performance on Arm based > machines - all other archs' maintainers are fine with PMU drivers using > dmesg. Good for them, although I'm pretty sure that at least the x86 folks are against this crap too. > > Anyway, I think this driver has bigger problems that need addressing. > > To me it represents yet another PMU driver submission - as the years go > by - that is lacking in the user messaging area. Which reminds me, can > you take another look at applying this?: As I said before, I'm not going to take anything that logs above pr_debug for things that are directly triggerable from userspace. Spin a version using pr_debug and I'll queue it. Have a good weekend, Will
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