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SubjectRe: [PATCH 1/8] perf: add PMU_RANGE_ATTR() helper for use by sw-like pmus
On 01/31/2014 09:58 PM, Michael Ellerman wrote:
> On Thu, 2014-16-01 at 23:53:47 UTC, Cody P Schafer wrote:
>> Add PMU_RANGE_ATTR() and PMU_RANGE_RESV() (for reserved areas) which
>> generate functions to extract the relevent bits from
>> event->attr.config{,1,2} for use by sw-like pmus where the
>> 'config{,1,2}' values don't map directly to hardware registers.
>
> This is neat.
>
> The split of the macros is a bit weird, ie. PMU_RANGE_RESV() doesn't really do
> what it's name suggests.
>
> I think you want one macro which creates the accessors, with a name that
> reflects that - yeah I can't think of a good one right now, but "event" should
> probably be in there because that's what it operates on.
>
> Having a macro for the reserved regions is good, but you MUST actually check
> that the reserved regions are zero. Otherwise you are permitting your caller to
> pass junk in there and you then can't unreserved them in a future version of
> the API.
>
> So I think a macro that gives you a special reserved region routine would be
> good, so you can write something like:
>
> if (event_check_reserved1() || event_check_reserved2())
> return -EINVAL;
>

The way it's set up right now, RESV is just a hint to the user of the
PMU_RANGE_ATTR() and PMU_RANGE_RESV() macros to indicate which to use.
RESV simply avoids creating an attr format which would go unused only in
the case where the range is a reserved one (and gcc would complain about
it).

I don't like the "event_check_foo()" bit because that is actually
identical to "event_get_foo()", I don't see a point in generating
differently named functions that do exactly the same thing.

The current user (hv-24x7.c) of PMU_RANGE_RESV() already does the
appropriate checking:

if (event_get_reserved1(event) ||
event_get_reserved2(event) ||
event_get_reserved3(event)) {
pr_devel("reserved set when forbidden 0x%llx(0x%llx) 0x%llx(0x%llx)
0x%llx(0x%llx)\n",
event->attr.config,
event_get_reserved1(event),
event->attr.config1,
event_get_reserved2(event),
event->attr.config2,
event_get_reserved3(event));
return -EINVAL;
}



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