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SubjectRe: [PATCH V2 08/11] coresight: core: Add support for dedicated percpu sinks
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On 1/15/21 2:36 AM, Anshuman Khandual wrote:
>
>
> On 1/13/21 3:13 PM, Suzuki K Poulose wrote:
>> On 1/13/21 4:18 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>
>>> ---
>>>   drivers/hwtracing/coresight/coresight-core.c | 14 ++++++++++++++
>>>   include/linux/coresight.h                    | 12 ++++++++++++
>>>   2 files changed, 26 insertions(+)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
>>> index 0062c89..b300606 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);
>>> +        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;
>>> @@ -998,6 +1006,12 @@ coresight_find_default_sink(struct coresight_device *csdev)
>>>   {
>>>       int depth = 0;
>>>   +    if (coresight_is_percpu_source(csdev)) {
>>
>> On a system without per_cpu sink, this would reset the default sink for the source device
>> every single time and fallback to searching every single time.
>
> Right.
>
>> So I think it would be better if did check if the def_sink was not set.
>> We could fold this into the case below may be. i.e,
>>
>>
>>     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);
>>     }
>>
>> Otherwise looks good to me.
>
> struct coresight_device *
> 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) {
> 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;
> }
>
> Would this be better instead ? coresight_find_sink() is invoked both when the
> source is not percpu (traditional coresight sources) and also as a fallback in
> case a percpu sink is not found for the percpu source device.
Yes, this is exactly what I proposed above.

Cheers
Suzuki

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