[tracing] Add feature param for perfetto buffer params

To experiment with data loss / performance balance.

bug: 40574594
Change-Id: I327c9281a717057cc36c8a4db38a8f3cbb74661c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6318180
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Mikhail Khokhlov <khokhlov@google.com>
Cr-Commit-Position: refs/heads/main@{#1427748}

services/tracing/public/cpp/perfetto/perfetto_tracing_backend.cc

@@ -8,6 +8,7 @@
 #include "base/command_line.h"
 #include "base/containers/flat_map.h"
 #include "base/containers/flat_set.h"
+#include "base/feature_list.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/raw_ptr.h"
 #include "base/memory/shared_memory_switch.h"
@@ -22,6 +23,7 @@
 #include "mojo/public/cpp/system/data_pipe_drainer.h"
 #include "services/tracing/public/cpp/perfetto/shared_memory.h"
 #include "services/tracing/public/cpp/perfetto/trace_packet_tokenizer.h"
+#include "services/tracing/public/cpp/tracing_features.h"
 #include "services/tracing/public/mojom/perfetto_service.mojom.h"
 #include "services/tracing/public/mojom/tracing_service.mojom.h"
 #include "third_party/perfetto/include/perfetto/base/task_runner.h"
@@ -40,15 +42,6 @@ using ShmemMode = perfetto::SharedMemoryArbiter::ShmemMode;
 namespace tracing {
 namespace {
 
-// TODO(crbug.com/40574593): Find a good compromise between performance and
-// data granularity (mainly relevant to running with small buffer sizes
-// when we use background tracing) on Android.
-#if BUILDFLAG(IS_ANDROID)
-constexpr size_t kDefaultSMBPageSizeBytes = 4 * 1024;
-#else
-constexpr size_t kDefaultSMBPageSizeBytes = 32 * 1024;
-#endif
-
 constexpr char kErrorTracingFailed[] = "Tracing failed";
 
 }  // namespace
@@ -686,9 +679,9 @@ PerfettoTracingBackend::ConnectProducer(const ConnectProducerArgs& args) {
   uint32_t shmem_size_hint = args.shmem_size_hint_bytes;
   uint32_t shmem_page_size_hint = args.shmem_page_size_hint_bytes;
   if (shmem_size_hint == 0)
-    shmem_size_hint = kDefaultSharedMemorySize;
+    shmem_size_hint = features::kPerfettoSharedMemorySizeBytes.Get();
   if (shmem_page_size_hint == 0)
-    shmem_page_size_hint = kDefaultSMBPageSizeBytes;
+    shmem_page_size_hint = features::kPerfettoSMBPageSizeBytes.Get();
 
   if (args.use_producer_provided_smb) {
     auto* command_line = base::CommandLine::ForCurrentProcess();

services/tracing/public/cpp/perfetto/shared_memory.h

@@ -14,9 +14,6 @@
 
 namespace tracing {
 
-// TODO(crbug.com/40574594): Figure out a good buffer size.
-inline constexpr size_t kDefaultSharedMemorySize = 4 * 1024 * 1024;  // 4 KB
-
 // This wraps //base's shmem implementation for Perfetto to consume.
 class COMPONENT_EXPORT(TRACING_CPP) ChromeBaseSharedMemory
     : public perfetto::SharedMemory {

services/tracing/public/cpp/trace_startup.cc

@@ -167,7 +167,8 @@ base::UnsafeSharedMemoryRegion CreateTracingOutputSharedMemory() {
   }
 #endif  // DCHECK_IS_ON()
 
-  auto shm = base::UnsafeSharedMemoryRegion::Create(kDefaultSharedMemorySize);
+  auto shm = base::UnsafeSharedMemoryRegion::Create(
+      features::kPerfettoSharedMemorySizeBytes.Get());
   if (!shm.IsValid()) {
     return base::UnsafeSharedMemoryRegion();
   }

services/tracing/public/cpp/trace_startup_shared_memory_unittest.cc

@@ -20,6 +20,7 @@
 #include "services/tracing/public/cpp/perfetto/shared_memory.h"
 #include "services/tracing/public/cpp/trace_startup.h"
 #include "services/tracing/public/cpp/trace_startup_config.h"
+#include "services/tracing/public/cpp/tracing_features.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/multiprocess_func_list.h"
 
@@ -41,7 +42,7 @@ TEST(TraceStartupSharedMemoryTest, Create) {
   auto shared_memory = CreateTracingOutputSharedMemory();
 
   ASSERT_TRUE(shared_memory.IsValid());
-  EXPECT_EQ(kDefaultSharedMemorySize, shared_memory.GetSize());
+  EXPECT_EQ(kDefaultSharedMemorySizeBytes, shared_memory.GetSize());
 }
 
 MULTIPROCESS_TEST_MAIN(InitFromLaunchParameters) {
@@ -82,7 +83,7 @@ MULTIPROCESS_TEST_MAIN(InitFromLaunchParameters) {
   auto shmem_region = base::shared_memory::UnsafeSharedMemoryRegionFrom(
       command_line->GetSwitchValueASCII(switches::kTraceBufferHandle));
   EXPECT_TRUE(shmem_region->IsValid());
-  EXPECT_EQ(kDefaultSharedMemorySize, shmem_region->GetSize());
+  EXPECT_EQ(kDefaultSharedMemorySizeBytes, shmem_region->GetSize());
 
   return 0;
 }

services/tracing/public/cpp/tracing_features.cc

@@ -20,6 +20,14 @@
 
 namespace features {
 
+namespace {
+
+BASE_FEATURE(kPerfettoBackendParams,
+             "kPerfettoBackendParams",
+             base::FEATURE_DISABLED_BY_DEFAULT);
+
+}  // namespace
+
 // Runs the tracing service as an in-process browser service.
 BASE_FEATURE(kTracingServiceInProcess,
              "TracingServiceInProcess",
@@ -44,6 +52,21 @@ BASE_FEATURE(kEnablePerfettoSystemBackgroundTracing,
              "EnablePerfettoSystemBackgroundTracing",
              base::FEATURE_DISABLED_BY_DEFAULT);
 
+// Controls the preferred size of each page in the shmem buffer.
+BASE_FEATURE_PARAM(int,
+                   kPerfettoSMBPageSizeBytes,
+                   &kPerfettoBackendParams,
+                   "page_size_bytes",
+                   tracing::kDefaultSMBPageSizeBytes);
+
+// Controls the size of the shared memory buffer between the current process and
+// the service backend(s)
+BASE_FEATURE_PARAM(int,
+                   kPerfettoSharedMemorySizeBytes,
+                   &kPerfettoBackendParams,
+                   "shared_memory_size_bytes",
+                   tracing::kDefaultSharedMemorySizeBytes);
+
 }  // namespace features
 
 namespace tracing {

services/tracing/public/cpp/tracing_features.h

@@ -10,6 +10,7 @@
 
 #include "base/component_export.h"
 #include "base/feature_list.h"
+#include "base/metrics/field_trial_params.h"
 
 namespace features {
 
@@ -24,10 +25,29 @@ extern const COMPONENT_EXPORT(TRACING_CPP) base::Feature
 extern const COMPONENT_EXPORT(TRACING_CPP) base::Feature
     kEnablePerfettoSystemBackgroundTracing;
 
+COMPONENT_EXPORT(TRACING_CPP)
+BASE_DECLARE_FEATURE_PARAM(int, kPerfettoSMBPageSizeBytes);
+
+COMPONENT_EXPORT(TRACING_CPP)
+BASE_DECLARE_FEATURE_PARAM(int, kPerfettoSharedMemorySizeBytes);
+
 }  // namespace features
 
 namespace tracing {
 
+// TODO(crbug.com/40574594): Figure out a good buffer size.
+inline constexpr size_t kDefaultSharedMemorySizeBytes =
+    4 * 1024 * 1024;  // 4 MB
+
+// TODO(crbug.com/40574593): Find a good compromise between performance and
+// data granularity (mainly relevant to running with small buffer sizes
+// when we use background tracing) on Android.
+#if BUILDFLAG(IS_ANDROID)
+inline constexpr size_t kDefaultSMBPageSizeBytes = 4 * 1024;
+#else
+inline constexpr size_t kDefaultSMBPageSizeBytes = 32 * 1024;
+#endif
+
 // Returns true if the system tracing Perfetto producer should be setup. This
 // can be influenced by the feature above or other situations (like debug
 // android builds).