[PATCH 2/2] coresight: etm-perf: Add AUX_NON_CONTIGUOUS_PAGES to cs_etm PMU

[Yabin Cui]

On Tue, Apr 22, 2025 at 7:21 AM Leo Yan <leo.yan at arm.com> wrote:
>
> On Mon, Apr 21, 2025 at 02:58:18PM -0700, Yabin Cui wrote:
> > The cs_etm PMU, regardless of the underlying trace sink (ETF, ETR or
> > TRBE), doesn't require contiguous pages for its AUX buffer.
>
> Though contiguous pages are not mandatory for TRBE, I would set the
> PERF_PMU_CAP_AUX_NO_SG flag for it.  This can potentially benefit
> performance.

As explained in the patch 1/2, my use case periodically collects ETM data
from the field (using both TRBE and ETR), and needs to reduce memory
fragmentation. If the performance impact is big, we can make it user
configurable. Otherwise, shall we default it to non-contiguous pages?

>
> For non per CPU sinks, it is fine to allocate non-contiguous pages.
>
> Thanks,
> Leo
>
> > This patch adds the PERF_PMU_CAP_AUX_NON_CONTIGUOUS_PAGES capability
> > to the cs_etm PMU. This allows the kernel to allocate non-contiguous
> > pages for the AUX buffer, reducing memory fragmentation when using
> > cs_etm.
> >
> > Signed-off-by: Yabin Cui <yabinc at google.com>
> > ---
> >  drivers/hwtracing/coresight/coresight-etm-perf.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > index f4cccd68e625..c98646eca7f8 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > @@ -899,7 +899,8 @@ int __init etm_perf_init(void)
> >       int ret;
> >
> >       etm_pmu.capabilities            = (PERF_PMU_CAP_EXCLUSIVE |
> > -                                        PERF_PMU_CAP_ITRACE);
> > +                                        PERF_PMU_CAP_ITRACE |
> > +                                        PERF_PMU_CAP_AUX_NON_CONTIGUOUS_PAGES);
> >
> >       etm_pmu.attr_groups             = etm_pmu_attr_groups;
> >       etm_pmu.task_ctx_nr             = perf_sw_context;
> > --
> > 2.49.0.805.g082f7c87e0-goog
> >
> >