Re: [PATCH RFC v1 0/4] perf: Introduce extended syscall error reporting

[Alexander Shishkin]

Ingo Molnar <mingo@xxxxxxxxxx> writes:

> * Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx> wrote:
>
>> Ingo Molnar <mingo@xxxxxxxxxx> writes:
>> 
>> > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> >
>> >> On Fri, Jul 24, 2015 at 02:45:55PM +0300, Alexander Shishkin wrote:
>> >> > Hi Peter and Ingo and everybody,
>> >> > 
>> >> > Here's my second stab at improving perf's error reporting by attaching
>> >> > arbitrary strings to the integer error codes. This is largely based
>> >> > off of the previous email thread [1].
>> >> > 
>> >> > This time around, I employed a linker trick to convert the structures
>> >> > containing extended error information into integers, which are then
>> >> > made to look just like normal error codes so that IS_ERR_VALUE() and
>> >> > friends would still work correctly on them. So no extra pointers in
>> >> > the struct perf_event or anywhere else; the extended error codes are
>> >> > passed around like normal error codes. They only need to be converted
>> >> > in syscalls' topmost return statements. This is done in 1/4.
>> >> > 
>> >> > Then, 2/4 illustrates how error sites can be extended to include more
>> >> > information such as file names and line numbers [1].
>> >> > 
>> >> > The other two patches add perf_err() annotation to a few semi-randomly
>> >> > picked places in perf core (3/4) and x86 bits (4/4).
>> >> 
>> >> Looks generally ok to me. Thanks for doing this.
>> >
>> > I like this too.
>> >
>> > Alexander, mind sending a finalized, signed off version?
>> 
>> Sure, I have everything ready, except for what about 2/4 (using 
>> CONFIG_DEBUG_KERNEL to extend output with file name and line number)? Should I 
>> leave it out or can we pick a more specific kconfig option or add a new one?
>
> I'd make it unconditional. We'll see whether we compress the debug info some more 
> if the number of callsites increases dramatically. Tooling can decide whether it 
> wants to display it by default, or print it only if some verbosity option is 
> activated.

Done.

> Also, mind structuring it in a bit more generic way that makes it possible for 
> other kernel subsystems to use this facility too? I.e. add a new header for it 
> instead of embedding it in perf, etc. Nothing complex, just some common-sense 
> generalization for a useful looking facility.

Yes, now I have both a perf specific and a more generic implementation
that perf then makes use of. Now let's arrive at a common denominator in
the other thread, I guess, and then we can go ahead with either version.

> For example the scheduler could start using it in struct sched_attr and feed back 
> the 15+ of failure causes in sys_sched_setattr() / __sched_setscheduler() in a bit 
> more usable fashion.

Yes, what I posted yesterday should be useful for this case as well.

Regards,
--
Alex
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