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Date: Fri, 7 Jun 2024 14:18:05 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: James Clark <james.clark@....com>, coresight@...ts.linaro.org,
gankulkarni@...amperecomputing.com, mike.leach@...aro.org,
leo.yan@...ux.dev, anshuman.khandual@....com
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>, John Garry
<john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-stm32@...md-mailman.stormreply.com, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 13/16] coresight: Use per-sink trace ID maps for Perf
sessions
Hi James
On 04/06/2024 15:30, James Clark wrote:
> This will allow sessions with more than CORESIGHT_TRACE_IDS_MAX ETMs
> as long as there are fewer than that many ETMs connected to each sink.
>
> Each sink owns its own trace ID map, and any Perf session connecting to
> that sink will allocate from it, even if the sink is currently in use by
> other users. This is similar to the existing behavior where the dynamic
> trace IDs are constant as long as there is any concurrent Perf session
> active. It's not completely optimal because slightly more IDs will be
> used than necessary, but the optimal solution involves tracking the PIDs
> of each session and allocating ID maps based on the session owner. This
> is difficult to do with the combination of per-thread and per-cpu modes
> and some scheduling issues. The complexity of this isn't likely to worth
> it because even with multiple users they'd just see a difference in the
> ordering of ID allocations rather than hitting any limits (unless the
> hardware does have too many ETMs connected to one sink).
Please find my comments below.
>
> Signed-off-by: James Clark <james.clark@....com>
> ---
> drivers/hwtracing/coresight/coresight-core.c | 10 ++++++++++
> drivers/hwtracing/coresight/coresight-dummy.c | 3 ++-
> drivers/hwtracing/coresight/coresight-etm-perf.c | 15 ++++++++++-----
> .../hwtracing/coresight/coresight-etm3x-core.c | 9 +++++----
> .../hwtracing/coresight/coresight-etm4x-core.c | 9 +++++----
> drivers/hwtracing/coresight/coresight-stm.c | 3 ++-
> drivers/hwtracing/coresight/coresight-sysfs.c | 3 ++-
> drivers/hwtracing/coresight/coresight-tpdm.c | 3 ++-
> include/linux/coresight.h | 3 ++-
> 9 files changed, 40 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 9fc6f6b863e0..d5aaeafe5c7d 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -902,6 +902,7 @@ static void coresight_device_release(struct device *dev)
> struct coresight_device *csdev = to_coresight_device(dev);
>
> fwnode_handle_put(csdev->dev.fwnode);
> + free_percpu(csdev->perf_sink_id_map.cpu_map);
> kfree(csdev);
> }
>
> @@ -1159,6 +1160,14 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
> dev_set_name(&csdev->dev, "%s", desc->name);
>
> + if (csdev->type == CORESIGHT_DEV_TYPE_SINK ||
> + csdev->type == CORESIGHT_DEV_TYPE_LINKSINK) {
> + csdev->perf_sink_id_map.cpu_map = alloc_percpu(atomic_t);
> + if (!csdev->perf_sink_id_map.cpu_map) {
> + ret = -ENOMEM;
> + goto err_out;
> + }
> + }
> /*
> * Make sure the device registration and the connection fixup
> * are synchronised, so that we don't see uninitialised devices
> @@ -1216,6 +1225,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> err_out:
> /* Cleanup the connection information */
> coresight_release_platform_data(NULL, desc->dev, desc->pdata);
> + kfree(csdev);
This hunk looked suspicious to me and is problematic. If we fail to
register the device with "device_register()", we already free the
csdev, via coresight_device_release() triggered via the device_put(),
(See comments in that case) and we could trigger a double free of the
csdev with this change.
I would recommend, you free the "csdev" in the above case, if we fail to
allocate the percpu storage and fall through.
> return ERR_PTR(ret);
> }
> EXPORT_SYMBOL_GPL(coresight_register);
> diff --git a/drivers/hwtracing/coresight/coresight-dummy.c b/drivers/hwtracing/coresight/coresight-dummy.c
> index ac70c0b491be..1f1b9ad160f6 100644
> --- a/drivers/hwtracing/coresight/coresight-dummy.c
> +++ b/drivers/hwtracing/coresight/coresight-dummy.c
> @@ -21,7 +21,8 @@ DEFINE_CORESIGHT_DEVLIST(source_devs, "dummy_source");
> DEFINE_CORESIGHT_DEVLIST(sink_devs, "dummy_sink");
>
> static int dummy_source_enable(struct coresight_device *csdev,
> - struct perf_event *event, enum cs_mode mode)
> + struct perf_event *event, enum cs_mode mode,
> + __maybe_unused struct coresight_trace_id_map *id_map)
> {
> dev_dbg(csdev->dev.parent, "Dummy source enabled\n");
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index c0c60e6a1703..7fb55dafb639 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -229,10 +229,13 @@ static void free_event_data(struct work_struct *work)
> struct list_head **ppath;
>
> ppath = etm_event_cpu_path_ptr(event_data, cpu);
> - if (!(IS_ERR_OR_NULL(*ppath)))
> + if (!(IS_ERR_OR_NULL(*ppath))) {
> + struct coresight_device *sink = coresight_get_sink(*ppath);
> +
> + coresight_trace_id_put_cpu_id_map(cpu, &sink->perf_sink_id_map);
> coresight_release_path(*ppath);
> + }
> *ppath = NULL;
> - coresight_trace_id_put_cpu_id(cpu);
> }
>
> /* mark perf event as done for trace id allocator */
> @@ -401,7 +404,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
> }
>
> /* ensure we can allocate a trace ID for this CPU */
> - trace_id = coresight_trace_id_get_cpu_id(cpu);
> + trace_id = coresight_trace_id_get_cpu_id_map(cpu, &sink->perf_sink_id_map);
> if (!IS_VALID_CS_TRACE_ID(trace_id)) {
> cpumask_clear_cpu(cpu, mask);
> coresight_release_path(path);
> @@ -495,7 +498,8 @@ static void etm_event_start(struct perf_event *event, int flags)
> goto fail_end_stop;
>
> /* Finally enable the tracer */
> - if (source_ops(csdev)->enable(csdev, event, CS_MODE_PERF))
> + if (source_ops(csdev)->enable(csdev, event, CS_MODE_PERF,
> + &sink->perf_sink_id_map))
> goto fail_disable_path;
>
> /*
> @@ -507,7 +511,8 @@ static void etm_event_start(struct perf_event *event, int flags)
> hw_id = FIELD_PREP(CS_AUX_HW_ID_VERSION_MASK,
> CS_AUX_HW_ID_CURR_VERSION);
> hw_id |= FIELD_PREP(CS_AUX_HW_ID_TRACE_ID_MASK,
> - coresight_trace_id_read_cpu_id(cpu));
> + coresight_trace_id_read_cpu_id_map(cpu,
> + &sink->perf_sink_id_map));
> perf_report_aux_output_id(event, hw_id);
> }
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> index 9d5c1391ffb1..65cf7456426a 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> @@ -481,7 +481,8 @@ void etm_release_trace_id(struct etm_drvdata *drvdata)
> }
>
> static int etm_enable_perf(struct coresight_device *csdev,
> - struct perf_event *event)
> + struct perf_event *event,
> + struct coresight_trace_id_map *id_map)
> {
> struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> int trace_id;
> @@ -500,7 +501,7 @@ static int etm_enable_perf(struct coresight_device *csdev,
> * with perf locks - we know the ID cannot change until perf shuts down
> * the session
> */
> - trace_id = coresight_trace_id_read_cpu_id(drvdata->cpu);
> + trace_id = coresight_trace_id_read_cpu_id_map(drvdata->cpu, id_map);
> if (!IS_VALID_CS_TRACE_ID(trace_id)) {
> dev_err(&drvdata->csdev->dev, "Failed to set trace ID for %s on CPU%d\n",
> dev_name(&drvdata->csdev->dev), drvdata->cpu);
> @@ -553,7 +554,7 @@ static int etm_enable_sysfs(struct coresight_device *csdev)
> }
>
> static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
> - enum cs_mode mode)
> + enum cs_mode mode, struct coresight_trace_id_map *id_map)
> {
> int ret;
> struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> @@ -568,7 +569,7 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
> ret = etm_enable_sysfs(csdev);
> break;
> case CS_MODE_PERF:
> - ret = etm_enable_perf(csdev, event);
> + ret = etm_enable_perf(csdev, event, id_map);
> break;
> default:
> ret = -EINVAL;
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index a0bdfabddbc6..fcd0f9ba562d 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -752,7 +752,8 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> }
>
> static int etm4_enable_perf(struct coresight_device *csdev,
> - struct perf_event *event)
> + struct perf_event *event,
> + struct coresight_trace_id_map *id_map)
> {
> int ret = 0, trace_id;
> struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> @@ -775,7 +776,7 @@ static int etm4_enable_perf(struct coresight_device *csdev,
> * with perf locks - we know the ID cannot change until perf shuts down
> * the session
> */
> - trace_id = coresight_trace_id_read_cpu_id(drvdata->cpu);
> + trace_id = coresight_trace_id_read_cpu_id_map(drvdata->cpu, id_map);
> if (!IS_VALID_CS_TRACE_ID(trace_id)) {
> dev_err(&drvdata->csdev->dev, "Failed to set trace ID for %s on CPU%d\n",
> dev_name(&drvdata->csdev->dev), drvdata->cpu);
> @@ -837,7 +838,7 @@ static int etm4_enable_sysfs(struct coresight_device *csdev)
> }
>
> static int etm4_enable(struct coresight_device *csdev, struct perf_event *event,
> - enum cs_mode mode)
> + enum cs_mode mode, struct coresight_trace_id_map *id_map)
> {
> int ret;
>
> @@ -851,7 +852,7 @@ static int etm4_enable(struct coresight_device *csdev, struct perf_event *event,
> ret = etm4_enable_sysfs(csdev);
> break;
> case CS_MODE_PERF:
> - ret = etm4_enable_perf(csdev, event);
> + ret = etm4_enable_perf(csdev, event, id_map);
> break;
> default:
> ret = -EINVAL;
> diff --git a/drivers/hwtracing/coresight/coresight-stm.c b/drivers/hwtracing/coresight/coresight-stm.c
> index e1c62820dfda..a80ad1de4c23 100644
> --- a/drivers/hwtracing/coresight/coresight-stm.c
> +++ b/drivers/hwtracing/coresight/coresight-stm.c
> @@ -194,7 +194,8 @@ static void stm_enable_hw(struct stm_drvdata *drvdata)
> }
>
> static int stm_enable(struct coresight_device *csdev, struct perf_event *event,
> - enum cs_mode mode)
> + enum cs_mode mode,
> + __maybe_unused struct coresight_trace_id_map *trace_id)
> {
> struct stm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
> index 1e67cc7758d7..a01c9e54e2ed 100644
> --- a/drivers/hwtracing/coresight/coresight-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-sysfs.c
> @@ -9,6 +9,7 @@
> #include <linux/kernel.h>
>
> #include "coresight-priv.h"
> +#include "coresight-trace-id.h"
>
> /*
> * Use IDR to map the hash of the source's device name
> @@ -63,7 +64,7 @@ static int coresight_enable_source_sysfs(struct coresight_device *csdev,
> */
> lockdep_assert_held(&coresight_mutex);
> if (coresight_get_mode(csdev) != CS_MODE_SYSFS) {
> - ret = source_ops(csdev)->enable(csdev, data, mode);
> + ret = source_ops(csdev)->enable(csdev, data, mode, NULL);
> if (ret)
> return ret;
> }
> diff --git a/drivers/hwtracing/coresight/coresight-tpdm.c b/drivers/hwtracing/coresight/coresight-tpdm.c
> index a9708ab0d488..0376ad326a2f 100644
> --- a/drivers/hwtracing/coresight/coresight-tpdm.c
> +++ b/drivers/hwtracing/coresight/coresight-tpdm.c
> @@ -439,7 +439,8 @@ static void __tpdm_enable(struct tpdm_drvdata *drvdata)
> }
>
> static int tpdm_enable(struct coresight_device *csdev, struct perf_event *event,
> - enum cs_mode mode)
> + enum cs_mode mode,
> + __maybe_unused struct coresight_trace_id_map *id_map)
> {
> struct tpdm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index 7d62b88bfb5c..9c3067e2e38b 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -290,6 +290,7 @@ struct coresight_device {
> bool sysfs_sink_activated;
> struct dev_ext_attribute *ea;
> struct coresight_device *def_sink;
> + struct coresight_trace_id_map perf_sink_id_map;
> /* sysfs links between components */
> int nr_links;
> bool has_conns_grp;
> @@ -384,7 +385,7 @@ struct coresight_ops_link {
> struct coresight_ops_source {
> int (*cpu_id)(struct coresight_device *csdev);
> int (*enable)(struct coresight_device *csdev, struct perf_event *event,
> - enum cs_mode mode);
> + enum cs_mode mode, struct coresight_trace_id_map *id_map);
I am slightly concerned by this change. We already pass down "event" for
a generic "enable" call back which serves both SYSFS & PERF. Now we are
adding one more, just for the PERF usage. Ideally, it is possible to
pass a single argument, e.g. perf_aux_output_handle which can fetch you
all the required infor for "enable".
i.e, hanlde->event, perf_get_aux(handle) -> event_data. We could even
add a helper to find the trace_id map from the handle, which could hide
the implementation details from the backend drivers.
e.g.,
etm_perf_get_trace_id_map(handle) -> {
event_data = perf_get_aux()
path = per_cpu(event_data->path)
sink = sink_from_path(path)
return trace_id of the sink;
}
That said, we if we intend to extend the usage of trace_id_map for
sysfs, this may be fine as is.
Suzuki
> void (*disable)(struct coresight_device *csdev,
> struct perf_event *event);
> };
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