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SubjectRe: [RFC PATCH] perfcounters: provide expansion room in the ABI

* Paul Mackerras <paulus@samba.org> wrote:

> Ingo Molnar wrote:
>
> > > git://git.kernel.org/pub/scm/linux/kernel/git/paulus/perfcounters.git rfc
> > >
> > > include/linux/perf_counter.h | 12 +++++++++---
> > > include/linux/syscalls.h | 2 +-
> > > kernel/perf_counter.c | 10 +++++++---
> > > 3 files changed, 17 insertions(+), 7 deletions(-)
> >
> > Pulled into tip:perfcounters/core, thanks Paul!
>
> Actually, I goofed slightly. In this bit of the patch:
>
> @@ -80,10 +81,15 @@ struct perf_counter_hw_event {
> exclude_user : 1, /* don't count user */
> exclude_kernel : 1, /* ditto kernel */
> exclude_hv : 1, /* ditto hypervisor */
> + exclude_idle : 1, /* don't count when idle */
>
> - __reserved_1 : 23;
> + __reserved_1 : 55;
> +
>
> the 55 should have been 54 if we want those bitfields to
> occupy 64 bits. With 55 there, __reserved_1 will go in the
> next 64-bit quadword (x86-speak, or doubleword in
> powerpc-speak).
>
> Do you think that's worth changing? If so I'll do a commit
> changing the 55 to 54.

How about extending it to 118 instead? The creation of a counter
is a slow path in any case.

Ingo


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