On Wed, Aug 19, 2020 at 02:34:14PM +0100, Alexandru Elisei wrote:
> From: Mark Rutland <mark.rutl...@arm.com>
>
> Currently we access the counter registers and their respective type
> registers indirectly. This requires us to write to PMSELR, issue an ISB,
> then access the relevant PMXEV* registers.
>
> This is unfortunate, because:
>
> * Under virtualization, accessing one register requires two traps to
> the hypervisor, even though we could access the register directly with
> a single trap.
>
> * We have to issue an ISB which we could otherwise avoid the cost of.
>
> * When we use NMIs, the NMI handler will have to save/restore the select
> register in case the code it preempted was attempting to access a
> counter or its type register.
>
> We can avoid these issues by directly accessing the relevant registers.
> This patch adds helpers to do so.
>
> In armv8pmu_enable_event() we still need the ISB to prevent the PE from
> reordering the write to PMINTENSET_EL1 register. If the interrupt is
> enabled before we disable the counter and the new event is configured,
> we might get an interrupt triggered by the previously programmed event
> overflowing, but which we wrongly attribute to the event that we are
> enabling.
>
> In the process, remove the comment that refers to the ARMv7 PMU.
>
> Cc: Julien Thierry <julien.thierry.k...@gmail.com>
> Cc: Will Deacon <will.dea...@arm.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
> Cc: Jiri Olsa <jo...@redhat.com>
> Cc: Namhyung Kim <namhy...@kernel.org>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Signed-off-by: Mark Rutland <mark.rutl...@arm.com>
> [Julien T.: Don't inline read/write functions to avoid big code-size
> increase, remove unused read_pmevtypern function,
> fix counter index issue.]
> Signed-off-by: Julien Thierry <julien.thie...@arm.com>
> [Removed comment, removed trailing semicolons in macros, added ISB]
nit: but it's customary to prefix these with your name, so it's easy to
figure out who made changes (like Julien did above).
(similar comment for other patches in this series)
> @@ -620,9 +686,14 @@ static void armv8pmu_enable_event(struct perf_event
> *event)
> * Disable counter
> */
> armv8pmu_disable_event_counter(event);
> + /*
> + * Make sure the effects of disabling the counter are visible before we
> + * start configuring the event.
> + */
> + isb();
With the isb() added by patch 1, why don't we just make these implicit
in armv8_{enable,disable}_event_counter() ?
Will
