Messages in this thread | | | Subject | Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration | From | Suzuki K Poulose <> | Date | Mon, 20 Aug 2018 15:36:47 +0100 |
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On 08/20/2018 03:22 PM, Kim Phillips wrote: > On Mon, 20 Aug 2018 11:03:03 +0100 > Suzuki K Poulose <suzuki.poulose@arm.com> wrote: > >> On 08/16/2018 08:28 PM, Mathieu Poirier wrote: >>> On Wed, 15 Aug 2018 at 09:28, Kim Phillips <kim.phillips@arm.com> wrote: >>>> >>>> On Wed, 15 Aug 2018 10:39:13 +0100 >>>> Will Deacon <will.deacon@arm.com> wrote: >>>> >>>>> 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@arm.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! >>>> >>>> That sounds technically self-contradicting to me. Why shouldn't >>>> coresight share the same policies as those used for PMU drivers? Or >>>> why not allow the individual vendor PMU driver authors control the >>>> level of user-friendliness of their own drivers? >>>> >>>> That being said, Matheiu, would you accept patches that make coresight >>>> more verbose in dmesg? >>> >>> It depends on the issue you're hoping to address. I'd rather see the >>> root cause of the problem fixed than adding temporary code. Suzuki >>> added the ETR perf API and I'm currently working on CPU-wide >>> scenarios. From there and with regards to what can happen in >>> setup_aux(), we should have things covered. >> >> I think the main issue is the lack of error code propagation from >> setup_aux() back to the perf_aux_output_handle_begin(), which always >> return -ENOMEM. If we fix that, we could get better idea of whats >> wrong. > > Why get a better idea when we can get the exact details?
The different values for error numbers are there for a reason...
> >> If someone is planning to add verbose messages, they may do so by adding >> dev_dbg() / pr_debug(), which can be turned on as and when needed. > > I disagree: that just adds another usage and kernel configuration > obstacle. Why not use pr_err straight up?
I personally don't agree to usage of pr_err() in paths which are easily triggered from user input. Also, we are moving all the "debugging" messages to the dynamic debug, to prevent lockdep splats.
Suzuki
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