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

[Yabin Cui]

On Thu, Apr 24, 2025 at 4:29 AM Anshuman Khandual
<anshuman.khandual at arm.com> wrote:
>
>
>
> On 4/24/25 01:31, Yabin Cui wrote:
> > 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?
>
> But is not that already happening ? cs_etm does not set the PMU cap
> PERF_PMU_CAP_AUX_NO_SG that means it can allocate non-contig memory
> chunk. Where am I missing ?

Although cs_etm doesn't set AUX_NO_SG flag, the perf component still prefers
to allocate contiguous AUX pages for it. The new flag is to ask perf
component to
not allocate contiguous AUX 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
> >>>
> >>>
> >