Re: [PATCH v3 00/12] perf/core: Generalise event exclusion checking

[Andrew Murray]

On Fri, Dec 07, 2018 at 05:25:17PM +0000, Will Deacon wrote:
> On Thu, Dec 06, 2018 at 04:47:17PM +0000, Andrew Murray wrote:
> > Many PMU drivers do not have the capability to exclude counting events
> > that occur in specific contexts such as idle, kernel, guest, etc. These
> > drivers indicate this by returning an error in their event_init upon
> > testing the events attribute flags.
> > 
> > However this approach requires that each time a new event modifier is
> > added to perf, all the perf drivers need to be modified to indicate that
> > they don't support the attribute. This results in additional boiler-plate
> > code common to many drivers that needs to be maintained. Furthermore the
> > drivers are not consistent with regards to the error value they return
> > when reporting unsupported attributes.
> > 
> > This patchset allow PMU drivers to advertise their inability to exclude
> > based on context via a new capability: PERF_PMU_CAP_NO_EXCLUDE. This
> > allows the perf core to reject requests for exclusion events where there
> > is no support in the PMU.
> > 
> > This is a functional change, in particular:
> > 
> >  - Some drivers will now additionally (but correctly) report unsupported
> >    exclusion flags. It's typical for existing userspace tools such as
> >    perf to handle such errors by retrying the system call without the
> >    unsupported flags.
> > 
> >  - Drivers that do not support any exclusion that previously reported
> >    -EPERM or -EOPNOTSUPP will now report -EINVAL - this is consistent
> >    with the majority and results in userspace perf retrying without
> >    exclusion.
> > 
> > All drivers touched by this patchset have been compile tested.
> 
> For the bits under arch/arm/ and drivers/perf:
> 
> Acked-by: Will Deacon <will.deacon@xxxxxxx>
> 
> Note that I've queued the TX2 uncore PMU for 4.21 [1], which could also
> benefit from your new flag.

Ah thanks for pointing this out, I'll send a patch in due course.

Thanks,

Andrwe Murray

> 
> Will
> 
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=for-next/perf&id=69c32972d59388c041268e8206e8eb1acff29b9a