Re: [PATCH V3 08/14] coresight: core: Add support for dedicated percpu sinks

Mathieu Poirier
2021-02-04T18:36:13Z

On Thu, Jan 28, 2021 at 09:16:34AM +0000, Suzuki K Poulose wrote:
> On 1/27/21 8:55 AM, Anshuman Khandual wrote:
> > Add support for dedicated sinks that are bound to individual CPUs. (e.g,
> > TRBE). To allow quicker access to the sink for a given CPU bound source,
> > keep a percpu array of the sink devices. Also, add support for building
> > a path to the CPU local sink from the ETM.
> >
> > This adds a new percpu sink type CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM.
> > This new sink type is exclusively available and can only work with percpu
> > source type device CORESIGHT_DEV_SUBTYPE_SOURCE_PERCPU_PROC.
> >
> > This defines a percpu structure that accommodates a single coresight_device
> > which can be used to store an initialized instance from a sink driver. As
> > these sinks are exclusively linked and dependent on corresponding percpu
> > sources devices, they should also be the default sink device during a perf
> > session.
> >
> > Outwards device connections are scanned while establishing paths between a
> > source and a sink device. But such connections are not present for certain
> > percpu source and sink devices which are exclusively linked and dependent.
> > Build the path directly and skip connection scanning for such devices.
> >
> > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Cc: Mike Leach <mike.leach@linaro.org>
> > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> > ---
> > Changes in V3:
> >
> > - Updated coresight_find_default_sink()
> >
> > drivers/hwtracing/coresight/coresight-core.c | 16 ++++++++++++++--
> > include/linux/coresight.h | 12 ++++++++++++
> > 2 files changed, 26 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> > index 0062c89..4795e28 100644
> > --- a/drivers/hwtracing/coresight/coresight-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > @@ -23,6 +23,7 @@
> > #include "coresight-priv.h"
> > static DEFINE_MUTEX(coresight_mutex);
> > +DEFINE_PER_CPU(struct coresight_device *, csdev_sink);
> > /**
> > * struct coresight_node - elements of a path, from source to sink
> > @@ -784,6 +785,13 @@ static int _coresight_build_path(struct coresight_device *csdev,
> > if (csdev == sink)
> > goto out;
> > + if (coresight_is_percpu_source(csdev) && coresight_is_percpu_sink(sink) &&
> > + sink == per_cpu(csdev_sink, source_ops(csdev)->cpu_id(csdev))) {
> > + _coresight_build_path(sink, sink, path);

The return value for _coresight_build_path() needs to be checked. Otherwise a
failure to allocate a node for the sink will go unoticed and make for a very
hard problem to debug.

> > + found = true;
> > + goto out;
> > + }
> > +
> > /* Not a sink - recursively explore each port found on this element */
> > for (i = 0; i < csdev->pdata->nr_outport; i++) {
> > struct coresight_device *child_dev;
> > @@ -999,8 +1007,12 @@ coresight_find_default_sink(struct coresight_device *csdev)
> > int depth = 0;
> > /* look for a default sink if we have not found for this device */
> > - if (!csdev->def_sink)
> > - csdev->def_sink = coresight_find_sink(csdev, &depth);
> > + if (!csdev->def_sink) {
> > + if (coresight_is_percpu_source(csdev))
> > + csdev->def_sink = per_cpu(csdev_sink, source_ops(csdev)->cpu_id(csdev));
> > + if (!csdev->def_sink)
> > + csdev->def_sink = coresight_find_sink(csdev, &depth);
> > + }
> > return csdev->def_sink;
> > }
> > diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> > index 976ec26..bc3a5ca 100644
> > --- a/include/linux/coresight.h
> > +++ b/include/linux/coresight.h
> > @@ -50,6 +50,7 @@ enum coresight_dev_subtype_sink {
> > CORESIGHT_DEV_SUBTYPE_SINK_PORT,
> > CORESIGHT_DEV_SUBTYPE_SINK_BUFFER,
> > CORESIGHT_DEV_SUBTYPE_SINK_SYSMEM,
> > + CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM,

Do we absolutely need to add a new sink type? It is only used in
_coresight_build_path() and that code could be:

if (coresight_is_percpu_source(csdev)) {
sink == per_cpu(csdev_sink, source_ops(csdev)->cpu_id(csdev));
if (sink && sink == csdev) {
_coresight_build_path(sink, sink, path);

> > };
> > enum coresight_dev_subtype_link {
> > @@ -428,6 +429,17 @@ static inline void csdev_access_write64(struct csdev_access *csa, u64 val, u32 o
> > csa->write(val, offset, false, true);
> > }
> > +static inline bool coresight_is_percpu_source(struct coresight_device *csdev)
> > +{
> > + return csdev && (csdev->type == CORESIGHT_DEV_TYPE_SOURCE) &&
> > + csdev->subtype.source_subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_PROC;
>
> Please add () around the last line. Same below.
>
> > +}
> > +
> > +static inline bool coresight_is_percpu_sink(struct coresight_device *csdev)
> > +{
> > + return csdev && (csdev->type == CORESIGHT_DEV_TYPE_SINK) &&
> > + csdev->subtype.sink_subtype == CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM;
> > +}
> > #else /* !CONFIG_64BIT */
> > static inline u64 csdev_access_relaxed_read64(struct csdev_access *csa,
> >
>
> With the above :
>
> Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>