Re: [RFC PATCH] MIPS: Oprofile: Drop support

[Matt Redfearn]

Hi Robert,

On 04/05/18 10:30, Robert Richter wrote:
> On 24.04.18 14:15:58, Matt Redfearn wrote:
> > On 24/04/18 14:05, James Hogan wrote:
> > > On Tue, Apr 24, 2018 at 01:55:54PM +0100, Matt Redfearn wrote:
> > > > Since it appears that MIPS oprofile support is currently broken, core
> > > > oprofile is not getting many updates and not as many architectures
> > > > implement support for it compared to perf, remove the MIPS support.
> > >
> > > That sounds reasonable to me. Any idea how long its been broken?
> >
> > Sorry, not yet. I haven't yet looked into where/how it's broken that would
> > narrow that down...
>
> oprofile moved to perf syscall as kernel i/f with version 1.0.0. The

OK interesting. I guess this was the point at which MIPS' current 
Kconfig rule which only allows building oprofile or perf into a kernel 
broke oprofile userspace.


> opcontrol script that was using the oprofile kernel i/f was removed:
>
>   https://sourceforge.net/p/oprofile/oprofile/ci/0c142c3a096d3e9ec42cc9b0ddad994fea60d135/
>
> Thus, cpus that do not support the perf syscall are no longer
> supported by 1.x releases.
>
>   https://sourceforge.net/p/oprofile/oprofile/ci/797d01dea0b82dbbdb0c21112a3de75990e011d2/
>
> For those remainings there is still version 0.9.x available (tagged
> PRE_RELEASE_1_0).
>
> I am undecided whether removing oprofile kernel i/f falls under the
> rule of "never break user space" here. Strictly seen, yes it breaks
> those remainings. So if the perf syscall is not available as an
> alternative, the oprofile kernel support shouldn't be removed.

perf is available for MIPS and supports many more CPU types than 
oprofile. oprofile userspace seemingly has been broken since 1.0.0 - 
removing oprofile support from the MIPS kernel would not break it more 
thatn it already is, but of course it would be better to fix it - if it 
is still useful and people still use it. That is the question that I was 
looking for answers for with this RFC - whether to spend the time & 
effort to fix oprofile, or if it can be removed since everyone uses perf.

Thanks,
Matt

> -Robert