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Commit a7cff515 authored by Nicolo' Mazzucato's avatar Nicolo' Mazzucato
Browse files

Limit concurrency SysUI bg coroutine dispatcher 

This limits the number of threads the systemui bg coroutine dispatcher can use. Before this change, the limit was the max between "kotlinx.coroutines.io.parallelism" and the number of cpus. In sysui we found traces with >40 threads and a lot of thread list lock contention. As the lock contention was also bocking the main thread, it ended up causing jank. The more SysUI switches work to be scheduled in the background, the more jank there would have been.

The value of available processor has been identified comparing unbounded, 5 and 10 bg threads. Available processors seem to provide the best values in terms of lock contention and jank.

Bug: 322437228
Bug: 321027720
Flag: None as this is fixing a recent regression already in the field.
Test: performance tests
Change-Id: I5b160fd69b8f3357d582420ef6713ae8cc2a43aa
parent 907c6167

packages/SystemUI/src/com/android/systemui/util/kotlin/SysUICoroutinesModule.kt

+29 −9
Original line number Diff line number Diff line
@@ -25,9 +25,13 @@ import dagger.Provides 
import kotlin.coroutines.CoroutineContext

import kotlinx.coroutines.CoroutineDispatcher

import kotlinx.coroutines.CoroutineScope

import kotlinx.coroutines.DelicateCoroutinesApi

import kotlinx.coroutines.Dispatchers

import kotlinx.coroutines.newFixedThreadPoolContext

import kotlinx.coroutines.plus



private const val LIMIT_BACKGROUND_DISPATCHER_THREADS = true



/** Providers for various SystemIU specific coroutines-related constructs. */

@Module

class SysUICoroutinesModule {
@@ -40,14 +44,13 @@ class SysUICoroutinesModule { 
    ): CoroutineScope = applicationScope.plus(coroutineContext)



    /**

     * Provide a [CoroutineDispatcher] backed by a thread pool containing at most X threads, where X

     * is the number of CPU cores available.

     *

     * Because there are multiple threads at play, there is no serialization order guarantee. You

     * should use a [kotlinx.coroutines.channels.Channel] for serialization if necessary.

     * Default Coroutine dispatcher for background operations.

     *

     * @see Dispatchers.Default

     * Note that this is explicitly limiting the number of threads. In the past, we used

     * [Dispatchers.IO]. This caused >40 threads to be spawned, and a lot of thread list lock

     * contention between then, eventually causing jank.

     */

    @OptIn(DelicateCoroutinesApi::class)

    @Provides

    @SysUISingleton

    @Background
@@ -55,12 +58,29 @@ class SysUICoroutinesModule { 
        "Use @Background CoroutineContext instead",

        ReplaceWith("bgCoroutineContext()", "kotlin.coroutines.CoroutineContext")

    )

    fun bgDispatcher(): CoroutineDispatcher = Dispatchers.IO

    fun bgDispatcher(): CoroutineDispatcher {

        return if (LIMIT_BACKGROUND_DISPATCHER_THREADS) {

            // Why a new ThreadPool instead of just using Dispatchers.IO with

            // CoroutineDispatcher.limitedParallelism? Because, if we were to use Dispatchers.IO, we

            // would share those threads with other dependencies using Dispatchers.IO.

            // Using a dedicated thread pool we have guarantees only SystemUI is able to schedule

            // code on those.

            newFixedThreadPoolContext(

                nThreads = Runtime.getRuntime().availableProcessors(),

                name = "SystemUIBg"

            )

        } else {

            Dispatchers.IO

        }

    }



    @Provides

    @Background

    @SysUISingleton

    fun bgCoroutineContext(@Tracing tracingCoroutineContext: CoroutineContext): CoroutineContext {

        return Dispatchers.IO + tracingCoroutineContext

    fun bgCoroutineContext(

        @Tracing tracingCoroutineContext: CoroutineContext,

        @Background bgCoroutineDispatcher: CoroutineDispatcher,

    ): CoroutineContext {

        return bgCoroutineDispatcher + tracingCoroutineContext

    }

}