kernel-shark: Hide CPUs with no data in them

A hash table, storring all idle CPUs is added to the session context.
If a CPU does not contain any data (is idle), its plot is not shown
by default when KernelShark starts. Note that, if the option '--cpu'
is used, it has priority and if idle CPUs are selected, the
corresponding empty CPU plots will be displayed.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215677
Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>

4 files changed, 21 insertions, 4 deletions

diff --git a/src/KsGLWidget.cpp b/src/KsGLWidget.cpp
index 3b2e0d4d..1c71ecbb 100644
--- a/src/KsGLWidget.cpp
+++ b/src/KsGLWidget.cpp
@@ -419,6 +419,7 @@ void KsGLWidget::keyReleaseEvent(QKeyEvent *event)
 
 void KsGLWidget::_defaultPlots(kshark_context *kshark_ctx)
 {
+	struct kshark_data_stream *stream;
 	QVector<int> streamIds, plotVec;
 	uint64_t tMin, tMax;
 	int nCPUs, nBins;
@@ -432,15 +433,19 @@ void KsGLWidget::_defaultPlots(kshark_context *kshark_ctx)
 	 */
 	streamIds = KsUtils::getStreamIdList(kshark_ctx);
 	for (auto const &sd: streamIds) {
-		nCPUs = kshark_ctx->stream[sd]->n_cpus;
+		stream = kshark_ctx->stream[sd];
+		nCPUs = stream->n_cpus;
 		plotVec.clear();
 
 		/* If the number of CPUs is too big show only the first 16. */
 		if (nCPUs > KS_MAX_START_PLOTS / kshark_ctx->n_streams)
 			nCPUs = KS_MAX_START_PLOTS / kshark_ctx->n_streams;
 
-		for (int i = 0; i < nCPUs; ++i)
-			plotVec.append(i);
+		for (int cpu{0}; cpu < stream->n_cpus && plotVec.count() < nCPUs; ++cpu) {
+			/* Do not add plots for idle CPUs. */
+			if (!kshark_hash_id_find(stream->idle_cpus, cpu))
+				plotVec.append(cpu);
+		}
 
 		_streamPlots[sd]._cpuList = plotVec;
 		_streamPlots[sd]._taskList = {};
diff --git a/src/libkshark-tepdata.c b/src/libkshark-tepdata.c
index 9740ed9c..e9244b07 100644
--- a/src/libkshark-tepdata.c
+++ b/src/libkshark-tepdata.c
@@ -391,7 +391,10 @@ static ssize_t get_records(struct kshark_context *kshark_ctx,
 			rec = tracecmd_read_data(kshark_get_tep_input(stream), cpu);
 		}
 
-		total += count;
+		if (!count)
+			kshark_hash_id_add(stream->idle_cpus, cpu);
+		else
+			total += count;
 	}
 
 	*rec_list = cpu_list;
diff --git a/src/libkshark.c b/src/libkshark.c
index 1222a815..44e553fe 100644
--- a/src/libkshark.c
+++ b/src/libkshark.c
@@ -121,6 +121,8 @@ static void kshark_stream_free(struct kshark_data_stream *stream)
 	if (!stream)
 		return;
 
+	kshark_hash_id_free(stream->idle_cpus);
+
 	kshark_hash_id_free(stream->show_task_filter);
 	kshark_hash_id_free(stream->hide_task_filter);
 
@@ -147,6 +149,8 @@ static struct kshark_data_stream *kshark_stream_alloc()
 	if (!stream)
 		goto fail;
 
+	stream->idle_cpus = kshark_hash_id_alloc(KS_FILTER_HASH_NBITS);
+
 	stream->show_task_filter = kshark_hash_id_alloc(KS_FILTER_HASH_NBITS);
 	stream->hide_task_filter = kshark_hash_id_alloc(KS_FILTER_HASH_NBITS);
 
@@ -433,6 +437,8 @@ static int kshark_stream_close(struct kshark_data_stream *stream)
 	kshark_hash_id_clear(stream->show_cpu_filter);
 	kshark_hash_id_clear(stream->hide_cpu_filter);
 
+	kshark_hash_id_clear(stream->idle_cpus);
+
 	if (kshark_is_tep(stream))
 		return kshark_tep_close_interface(stream);
 
diff --git a/src/libkshark.h b/src/libkshark.h
index 23e3b492..1514f332 100644
--- a/src/libkshark.h
+++ b/src/libkshark.h
@@ -286,6 +286,9 @@ struct kshark_data_stream {
 	/** The number of CPUs presented in this data stream. */
 	int			n_cpus;
 
+	/** Hash table of Idle CPUs. */
+	struct kshark_hash_id	*idle_cpus;
+
 	/**
 	 * The number of distinct event types presented in this data stream.
 	 */