Prevent iOS daemon throttling with SSH launch and priority boosts

iOS aggressively throttles daemon processes, causing CADisplayLink callbacks to be delayed or skipped. This commit implements multiple workarounds: - Replace CADisplayLink with high-priority dispatch timer (QOS_CLASS_USER_INTERACTIVE) - Add power assertions to prevent display/GPU/CPU throttling - Launch daemon via SSH to localhost for better scheduler treatment - Set real-time thread priority and ProcessType=Interactive - Add FPS diagnostics logging to monitor capture performance - Auto-setup passwordless SSH keys during package installation 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
2025-12-08 08:12:48 +05:00
parent aecc88aed2
commit 6d5d143dd9
6 changed files with 194 additions and 20 deletions
--- a/screendump/FrameUpdater.m
+++ b/screendump/FrameUpdater.m
@@ -1,4 +1,5 @@
 #import "FrameUpdater.h"
+#import <mach/mach_time.h>

@implementation FrameUpdater {

@@ -6,6 +7,7 @@
 	NSOperationQueue *_q;
 	BOOL _updatingFrames;
 	CADisplayLink *_displayLink;
+	dispatch_source_t _timer;

 	// Shared from ScreenDumpVNC
 	IOSurfaceRef _screenSurface;
@@ -20,6 +22,14 @@
 	// Dual capture mode support
 	IOSurfaceRef _renderServerSurface; // Separate surface for CARenderServer (avoids framebuffer locking)
 	CaptureMode(^_captureModeBlock)(void);
+
+	// Diagnostics
+	uint64_t _timerFires;
+	uint64_t _framesRendered;
+	uint64_t _framesSkipped;
+	uint64_t _lastStatsTime;
+	uint64_t _totalCaptureTime;
+	uint64_t _maxCaptureTime;
 }

 -(instancetype)initWithSurfaceInfo:(IOSurfaceRef)screenSurface
@@ -35,6 +45,7 @@
 	if ((self = [super init])) {
 		_q = [[NSOperationQueue alloc] init];
 		_q.maxConcurrentOperationCount = 1; // Serialize to prevent frame queue buildup
+		_q.qualityOfService = NSQualityOfServiceUserInteractive;
 		_updatingFrames = NO;
 		_displayLink = nil;

@@ -60,12 +71,19 @@
 		return;
 	}

+	_timerFires++;
+
 	// Skip if queue is busy to prevent frame buildup and reduce lock contention
 	if (_q.operationCount > 0) {
+		_framesSkipped++;
 		return;
 	}

 	[_q addOperationWithBlock: ^{
+		_framesRendered++;
+
+		uint64_t captureStart = mach_absolute_time();
+
 		// Get current capture mode
 		CaptureMode mode = _captureModeBlock ? _captureModeBlock() : CaptureModeCARenderServer;
 		BOOL needsScaling = (_width != _nativeWidth || _height != _nativeHeight);
@@ -86,28 +104,78 @@
 			}
 		}

+		uint64_t captureEnd = mach_absolute_time();
+		uint64_t captureDuration = captureEnd - captureStart;
+		_totalCaptureTime += captureDuration;
+		if (captureDuration > _maxCaptureTime) _maxCaptureTime = captureDuration;
+
 		rfbMarkRectAsModified(_rfbScreenInfo, 0, 0, _width, _height);
+
+		// Log stats every second
+		uint64_t now = mach_absolute_time();
+		if (_lastStatsTime == 0) _lastStatsTime = now;
+
+		mach_timebase_info_data_t timebase;
+		mach_timebase_info(&timebase);
+		uint64_t elapsed_ns = (now - _lastStatsTime) * timebase.numer / timebase.denom;
+
+		if (elapsed_ns >= NSEC_PER_SEC) {
+			double elapsed_sec = (double)elapsed_ns / NSEC_PER_SEC;
+			double avgCaptureMs = (_framesRendered > 0) ?
+				((double)_totalCaptureTime * timebase.numer / timebase.denom / _framesRendered / 1000000.0) : 0;
+			double maxCaptureMs = (double)_maxCaptureTime * timebase.numer / timebase.denom / 1000000.0;
+
+			NSLog(@"[FPS] fps=%.1f skip=%.0f%% | capture: avg=%.1fms max=%.1fms",
+				  _framesRendered / elapsed_sec,
+				  (_timerFires > 0) ? (100.0 * _framesSkipped / _timerFires) : 0.0,
+				  avgCaptureMs, maxCaptureMs);
+			_timerFires = 0;
+			_framesRendered = 0;
+			_framesSkipped = 0;
+			_totalCaptureTime = 0;
+			_maxCaptureTime = 0;
+			_lastStatsTime = now;
+		}
 	}];
 }

 -(void)stopFrameLoop {
-	if (_displayLink == nil) return;
+	_updatingFrames = NO;

+	if (_timer) {
+		dispatch_source_cancel(_timer);
+		_timer = nil;
+	}
+
+	if (_displayLink) {
 		dispatch_async(dispatch_get_main_queue(), ^(void){
 			[_displayLink invalidate];
 			_displayLink = nil;
-		_updatingFrames = NO;
 		});
+	}
 }

 -(void)startFrameLoop {
 	[self stopFrameLoop];
 	_updatingFrames = YES;

-	CADisplayLink *displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(_updateFrame)];
-	displayLink.preferredFramesPerSecond = 60; // Limit to 60 FPS
-	[displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
-	_displayLink = displayLink;
+	// Use high-priority dispatch timer instead of CADisplayLink
+	// CADisplayLink may be throttled for daemon processes
+	dispatch_queue_attr_t attr = dispatch_queue_attr_make_with_qos_class(
+		DISPATCH_QUEUE_SERIAL, QOS_CLASS_USER_INTERACTIVE, 0);
+	dispatch_queue_t timerQueue = dispatch_queue_create("com.mousen.screendump.frametimer", attr);
+
+	_timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, DISPATCH_TIMER_STRICT, timerQueue);
+
+	// 60 FPS = ~16.67ms interval
+	uint64_t interval = NSEC_PER_SEC / 60;
+	dispatch_source_set_timer(_timer, dispatch_time(DISPATCH_TIME_NOW, 0), interval, 0);
+
+	dispatch_source_set_event_handler(_timer, ^{
+		[self _updateFrame];
+	});
+
+	dispatch_resume(_timer);
 }

 -(void)dealloc {
--- a/screendump/Makefile
+++ b/screendump/Makefile
@@ -2,19 +2,20 @@ export THEOS_PACKAGE_SCHEME = rootless
 export ARCHS = arm64
 export TARGET = iphone:16.5:14.0
 export GO_EASY_ON_ME = 1
-export COPYFILE_DISABLE=1
+export COPYFILE_DISABLE = 1

 include $(THEOS)/makefiles/common.mk

 TOOL_NAME = screendumpd
-$(TOOL_NAME)_FILES = $(wildcard *.m)
-$(TOOL_NAME)_FRAMEWORKS := IOSurface IOKit
-$(TOOL_NAME)_PRIVATE_FRAMEWORKS := IOMobileFramebuffer IOSurface
-$(TOOL_NAME)_OBJCFLAGS += -I./vncbuild/include -Iinclude -fobjc-arc
-$(TOOL_NAME)_LDFLAGS += -Wl,-segalign,4000 -L./vncbuild/lib  -lvncserver -lpng -llzo2 -ljpeg -lssl -lcrypto -lz
-$(TOOL_NAME)_CFLAGS = -w
-$(TOOL_NAME)_CODESIGN_FLAGS = "-Sen.plist"
-$(TOOL_NAME)_INSTALL_PATH = /usr/libexec
+
+screendumpd_FILES = $(wildcard *.m)
+screendumpd_FRAMEWORKS = IOSurface IOKit
+screendumpd_PRIVATE_FRAMEWORKS = IOMobileFramebuffer IOSurface
+screendumpd_OBJCFLAGS = -I./vncbuild/include -Iinclude -fobjc-arc
+screendumpd_LDFLAGS = -Wl,-segalign,4000 -L./vncbuild/lib -lvncserver -lpng -llzo2 -ljpeg -lssl -lcrypto -lz
+screendumpd_CFLAGS = -w
+screendumpd_CODESIGN_FLAGS = -Sen.plist
+screendumpd_INSTALL_PATH = /usr/libexec

 before-stage::
 	$(ECHO_NOTHING)find . -name '.DS_Store' -type f -delete$(ECHO_END)
--- a/screendump/ScreenDumpVNC.m
+++ b/screendump/ScreenDumpVNC.m
@@ -5,6 +5,7 @@
 #import <UIKit/UIKit.h>
 #import <rfb/rfb.h>
 #import "IOMobileFramebuffer.h"
+#import <IOKit/pwr_mgt/IOPMLib.h>

@implementation ScreenDumpVNC {
 	int _prefsHeight;
@@ -38,6 +39,25 @@
 +(void)load {
 	ScreenDumpVNC* sharedInstance = [self sharedInstance];
 	if (![sharedInstance enabled]) return;
+
+	// Tell iOS this is latency-critical work - prevents throttling for daemons
+	[[NSProcessInfo processInfo] beginActivityWithOptions:(NSActivityLatencyCritical | NSActivityUserInitiated)
+												   reason:@"VNC screen streaming"];
+
+	// Power assertion to prevent display/GPU throttling
+	IOPMAssertionID assertionID;
+	IOPMAssertionCreateWithName(kIOPMAssertionTypePreventUserIdleDisplaySleep,
+								kIOPMAssertionLevelOn,
+								CFSTR("VNC screen capture requires display access"),
+								&assertionID);
+
+	// Also assert we need system activity (prevents CPU throttling)
+	IOPMAssertionID systemAssertionID;
+	IOPMAssertionCreateWithName(kIOPMAssertionTypePreventUserIdleSystemSleep,
+								kIOPMAssertionLevelOn,
+								CFSTR("VNC server active"),
+								&systemAssertionID);
+
 	[sharedInstance setupScreenInfo];
 	[sharedInstance startVNCServer];
 }
--- a/screendump/layout/DEBIAN/postinst
+++ b/screendump/layout/DEBIAN/postinst
@@ -1,3 +1,40 @@
 #!/bin/sh
+
+# Setup passwordless SSH for root to localhost (required for screendumpd performance)
+SSH_DIR="/var/jb/var/root/.ssh"
+KEY_FILE="$SSH_DIR/id_ed25519"
+AUTH_KEYS="$SSH_DIR/authorized_keys"
+
+# Create .ssh directory if it doesn't exist
+if [ ! -d "$SSH_DIR" ]; then
+    mkdir -p "$SSH_DIR"
+    chmod 700 "$SSH_DIR"
+fi
+
+# Generate ed25519 key if it doesn't exist
+if [ ! -f "$KEY_FILE" ]; then
+    ssh-keygen -t ed25519 -N "" -f "$KEY_FILE" -q
+    chmod 600 "$KEY_FILE"
+    chmod 644 "${KEY_FILE}.pub"
+fi
+
+# Add public key to authorized_keys if not already present
+if [ -f "${KEY_FILE}.pub" ]; then
+    PUB_KEY=$(cat "${KEY_FILE}.pub")
+
+    # Create authorized_keys if it doesn't exist
+    if [ ! -f "$AUTH_KEYS" ]; then
+        touch "$AUTH_KEYS"
+        chmod 600 "$AUTH_KEYS"
+    fi
+
+    # Check if key is already in authorized_keys
+    if ! grep -qF "$PUB_KEY" "$AUTH_KEYS" 2>/dev/null; then
+        echo "$PUB_KEY" >> "$AUTH_KEYS"
+    fi
+fi
+
+# Load the launch daemon
 launchctl load /var/jb/Library/LaunchDaemons/com.mousen.screendumpd.plist 2> /dev/null
-exit 0;
+
+exit 0
--- a/screendump/layout/Library/LaunchDaemons/com.mousen.screendumpd.plist
+++ b/screendump/layout/Library/LaunchDaemons/com.mousen.screendumpd.plist
@@ -6,6 +6,14 @@
 	<string>com.mousen.screendumpd</string>
 	<key>ProgramArguments</key>
 	<array>
+		<string>/var/jb/usr/bin/ssh</string>
+		<string>-o</string>
+		<string>StrictHostKeyChecking=no</string>
+		<string>-o</string>
+		<string>UserKnownHostsFile=/dev/null</string>
+		<string>-o</string>
+		<string>BatchMode=yes</string>
+		<string>root@localhost</string>
 		<string>/var/jb/usr/libexec/screendumpd</string>
 	</array>
 	<key>RunAtLoad</key>
@@ -22,5 +30,13 @@
        <key>Core</key>
 		<integer>9223372036854775807</integer>
 	</dict>
+	<key>ProcessType</key>
+	<string>Interactive</string>
+	<key>Nice</key>
+	<integer>-10</integer>
+	<key>LegacyTimers</key>
+	<true/>
+	<key>UserName</key>
+	<string>root</string>
 </dict>
 </plist>
--- a/screendump/main.m
+++ b/screendump/main.m
@@ -1,12 +1,44 @@
 #import <Foundation/Foundation.h>
 #import <stdio.h>
+#import <signal.h>
+#import <unistd.h>
+#import <pthread.h>
+#import <sched.h>
+#import <dispatch/dispatch.h>
 #import "ScreenDumpVNC.h"
 #import "utils.h"

 #define kPreferencesNotify "com.mousen.screendump/restart"

+static void signalHandler(int sig) {
+	exit(0);
+}
+
 int main(int argc, char *argv[], char *envp[]) {
 	@autoreleasepool {
+		// Handle termination signals (sent by launchd or when SSH disconnects)
+		signal(SIGTERM, signalHandler);
+		signal(SIGHUP, signalHandler);
+		signal(SIGINT, signalHandler);
+
+		// Monitor parent process - exit if parent (sshd) dies (ppid becomes 1)
+		pid_t originalPpid = getppid();
+		dispatch_source_t parentTimer = dispatch_source_create(
+			DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0));
+		dispatch_source_set_timer(parentTimer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 0);
+		dispatch_source_set_event_handler(parentTimer, ^{
+			if (getppid() != originalPpid) {
+				// Parent changed (likely died and we got reparented to launchd/init)
+				exit(0);
+			}
+		});
+		dispatch_resume(parentTimer);
+
+		// Boost main thread to real-time priority for better daemon performance
+		struct sched_param param;
+		param.sched_priority = sched_get_priority_max(SCHED_RR);
+		pthread_setschedparam(pthread_self(), SCHED_RR, &param);
+
 		CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), NULL, (CFNotificationCallback)exitProcess, CFSTR(kPreferencesNotify), NULL, CFNotificationSuspensionBehaviorDeliverImmediately);

        [ScreenDumpVNC load];