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Message-ID: <CAJ9a7VghourELWQokjDgydwsBObKCg_Puh8zD2L=QiX=RUb=0g@mail.gmail.com>
Date: Mon, 8 Mar 2021 17:25:46 +0000
From: Mike Leach <mike.leach@...aro.org>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Anshuman Khandual <anshuman.khandual@....com>,
Leo Yan <leo.yan@...aro.org>,
Linu Cherian <lcherian@...vell.com>
Subject: Re: [PATCH v4 10/19] coresight: etm-perf: Allow an event to use
different sinks
On Thu, 25 Feb 2021 at 19:36, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>
> When a sink is not specified by the user, the etm perf driver
> finds a suitable sink automatically, based on the first ETM
> where this event could be scheduled. Then we allocate the
> sink buffer based on the selected sink. This is fine for a
> CPU bound event as the "sink" is always guaranteed to be
> reachable from the ETM (as this is the only ETM where the
> event is going to be scheduled). However, if we have a thread
> bound event, the event could be scheduled on any of the ETMs
> on the system. In this case, currently we automatically select
> a sink and exclude any ETMs that cannot reach the selected
> sink. This is problematic especially for 1x1 configurations.
> We end up in tracing the event only on the "first" ETM,
> as the default sink is local to the first ETM and unreachable
> from the rest. However, we could allow the other ETMs to
> trace if they all have a sink that is compatible with the
> "selected" sink and can use the sink buffer. This can be
> easily done by verifying that they are all driven by the
> same driver and matches the same subtype. Please note
> that at anytime there can be only one ETM tracing the event.
>
> Adding support for different types of sinks for a single
> event is complex and is not something that we expect
> on a sane configuration.
>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Tested-by: Linu Cherian <lcherian@...vell.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
> Changes:
> - Rename sinks_match => sinks_compatible
> - Tighten the check by matching the sink subtype
> - Use user_sink instead of "sink_forced" and clean up the code (Mathieu)
> - More comments, better commit description
> ---
> .../hwtracing/coresight/coresight-etm-perf.c | 60 ++++++++++++++++---
> 1 file changed, 52 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index 0f603b4094f2..aa0974bd265b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -232,6 +232,25 @@ static void etm_free_aux(void *data)
> schedule_work(&event_data->work);
> }
>
> +/*
> + * Check if two given sinks are compatible with each other,
> + * so that they can use the same sink buffers, when an event
> + * moves around.
> + */
> +static bool sinks_compatible(struct coresight_device *a,
> + struct coresight_device *b)
> +{
> + if (!a || !b)
> + return false;
> + /*
> + * If the sinks are of the same subtype and driven
> + * by the same driver, we can use the same buffer
> + * on these sinks.
> + */
> + return (a->subtype.sink_subtype == b->subtype.sink_subtype) &&
> + (sink_ops(a) == sink_ops(b));
> +}
> +
> static void *etm_setup_aux(struct perf_event *event, void **pages,
> int nr_pages, bool overwrite)
> {
> @@ -239,6 +258,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
> int cpu = event->cpu;
> cpumask_t *mask;
> struct coresight_device *sink = NULL;
> + struct coresight_device *user_sink = NULL, *last_sink = NULL;
> struct etm_event_data *event_data = NULL;
>
> event_data = alloc_event_data(cpu);
> @@ -249,7 +269,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
> /* First get the selected sink from user space. */
> if (event->attr.config2) {
> id = (u32)event->attr.config2;
> - sink = coresight_get_sink_by_id(id);
> + sink = user_sink = coresight_get_sink_by_id(id);
> }
>
> mask = &event_data->mask;
> @@ -277,14 +297,33 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
> }
>
> /*
> - * No sink provided - look for a default sink for one of the
> - * devices. At present we only support topology where all CPUs
> - * use the same sink [N:1], so only need to find one sink. The
> - * coresight_build_path later will remove any CPU that does not
> - * attach to the sink, or if we have not found a sink.
> + * No sink provided - look for a default sink for all the ETMs,
> + * where this event can be scheduled.
> + * We allocate the sink specific buffers only once for this
> + * event. If the ETMs have different default sink devices, we
> + * can only use a single "type" of sink as the event can carry
> + * only one sink specific buffer. Thus we have to make sure
> + * that the sinks are of the same type and driven by the same
> + * driver, as the one we allocate the buffer for. As such
> + * we choose the first sink and check if the remaining ETMs
> + * have a compatible default sink. We don't trace on a CPU
> + * if the sink is not compatible.
> */
> - if (!sink)
> + if (!user_sink) {
> + /* Find the default sink for this ETM */
> sink = coresight_find_default_sink(csdev);
> + if (!sink) {
> + cpumask_clear_cpu(cpu, mask);
> + continue;
> + }
> +
> + /* Check if this sink compatible with the last sink */
> + if (last_sink && !sinks_compatible(last_sink, sink)) {
> + cpumask_clear_cpu(cpu, mask);
> + continue;
> + }
> + last_sink = sink;
> + }
>
> /*
> * Building a path doesn't enable it, it simply builds a
> @@ -312,7 +351,12 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
> if (!sink_ops(sink)->alloc_buffer || !sink_ops(sink)->free_buffer)
> goto err;
>
> - /* Allocate the sink buffer for this session */
> + /*
> + * Allocate the sink buffer for this session. All the sinks
> + * where this event can be scheduled are ensured to be of the
> + * same type. Thus the same sink configuration is used by the
> + * sinks.
> + */
> event_data->snk_config =
> sink_ops(sink)->alloc_buffer(sink, event, pages,
> nr_pages, overwrite);
> --
> 2.24.1
>
Reviewed-by: Mike Leach <mike.leach@...aro.org>
--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK
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