Mathieu Poirier <mathieu.poir...@linaro.org> writes:
> Variable 'max_order' needs to be initialised to log2 of the
> number of pages invariant of the no scather-gather PMU option.
> Otherwise 'rb_alloc_aux_page' gets an order that is equal to
> '0', which prevents the private page information to be set
> properly.
But that wouldn't make sense: we're only using the private field in
pages at the bottom of high-order allocations, which only ever happen
for NO_SG devices. Otherwise, every page is the buffer is just an
individual page and doesn't need anything in the private field.
> Signed-off-by: Mathieu Poirier <mathieu.poir...@linaro.org>
> ---
> kernel/events/ring_buffer.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 96472824a752..bd3da7bebe9e 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -449,18 +449,18 @@ int rb_alloc_aux(struct ring_buffer *rb, struct
> perf_event *event,
> {
> bool overwrite = !(flags & RING_BUFFER_WRITABLE);
> int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
> - int ret = -ENOMEM, max_order = 0;
> + int ret = -ENOMEM, max_order;
>
> if (!has_aux(event))
> return -ENOTSUPP;
>
> - if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
> - /*
> - * We need to start with the max_order that fits in nr_pages,
> - * not the other way around, hence ilog2() and not get_order.
> - */
> - max_order = ilog2(nr_pages);
> + /*
> + * We need to start with the max_order that fits in nr_pages,
> + * not the other way around, hence ilog2() and not get_order.
> + */
> + max_order = ilog2(nr_pages);
Also, nr_pages here is the whole buffer, but when we do use
page::private, we put an each individual high-order allocation's order
there, not the whole buffer's, which makes sense because you'd need to
know the former to program the HW properly, whereas the latter you'd get
as a parameter to pmu::setup_aux() callback anyway.
Regards,
--
Alex
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