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 <redacted>

Note that I've queued the TX2 uncore PMU for 4.21 [1], which could also
benefit from your new flag.

Will

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