settings: add default.clock.quantum-floor property

Remove some of the hardcoded values (the absolute smallest buffer size,
independent on the sample rate) to a config option. Set it to the
default value of 4, like what it was before.

Change the hardcoded absolute lowest limit to 1 because anything else
does not make sense.

Enforce the quantum-floor when calculating the final graph quantum.

Fixes #3908

doc/dox/config/pipewire.conf.5.md

@@ -177,7 +177,8 @@ the quantums.
 It is possible to specify up to 32 alternative sample rates. The graph
 sample rate will be switched when devices are idle. Note that this is
 not enabled by default for now because of various kernel and Bluetooth
-issues.
+issues. Note that the min/max/default quantum values are scaled when
+the samplerate changes.
 
 @PAR@ pipewire.conf  default.clock.min-quantum = 32
 Default minimum quantum.
@@ -189,7 +190,12 @@ Default maximum quantum.
 Default quantum used when no client specifies one.
 
 @PAR@ pipewire.conf  default.clock.quantum-limit = 8192
-Maximum quantum to reserve space for.
+Maximum quantum to reserve space for. This is the maximum buffer size used
+in the graph, regardless of the samplerate.
+
+@PAR@ pipewire.conf  default.clock.quantum-floor = 4
+Minimum quantum to reserve space for. This is the minimum buffer size used
+in the graph, regardless of the samplerate.
 
 @PAR@ pipewire.conf  default.video.width
 Default video width

src/daemon/minimal.conf.in

@@ -32,6 +32,7 @@ context.properties = {
     #default.clock.min-quantum   = 32
     #default.clock.max-quantum   = 2048
     #default.clock.quantum-limit = 8192
+    #default.clock.quantum-floor = 4
     #default.video.width         = 640
     #default.video.height        = 480
     #default.video.rate.num      = 25

src/daemon/pipewire.conf.in

@@ -32,6 +32,7 @@ context.properties = {
     #default.clock.min-quantum   = 32
     #default.clock.max-quantum   = 2048
     #default.clock.quantum-limit = 8192
+    #default.clock.quantum-floor = 4
     #default.video.width         = 640
     #default.video.height        = 480
     #default.video.rate.num      = 25

src/pipewire/context.c

@@ -994,7 +994,7 @@ static void remove_from_driver(struct pw_context *context, struct spa_list *node
 }
 
 static inline void get_quantums(struct pw_context *context, uint32_t *def,
-		uint32_t *min, uint32_t *max, uint32_t *limit, uint32_t *rate)
+		uint32_t *min, uint32_t *max, uint32_t *rate, uint32_t *floor, uint32_t *ceil)
 {
 	struct settings *s = &context->settings;
 	if (s->clock_force_quantum != 0) {
@@ -1006,7 +1006,8 @@ static inline void get_quantums(struct pw_context *context, uint32_t *def,
 		*max = s->clock_max_quantum;
 		*rate = s->clock_rate;
 	}
-	*limit = s->clock_quantum_limit;
+	*floor = s->clock_quantum_floor;
+	*ceil = s->clock_quantum_limit;
 }
 
 static inline const uint32_t *get_rates(struct pw_context *context, uint32_t *def, uint32_t *n_rates,
@@ -1199,7 +1200,7 @@ int pw_context_recalc_graph(struct pw_context *context, const char *reason)
 	struct settings *settings = &context->settings;
 	struct pw_impl_node *n, *s, *target, *fallback;
 	const uint32_t *rates;
-	uint32_t max_quantum, min_quantum, def_quantum, lim_quantum, rate_quantum;
+	uint32_t max_quantum, min_quantum, def_quantum, rate_quantum, floor_quantum, ceil_quantum;
 	uint32_t n_rates, def_rate;
 	bool freewheel = false, global_force_rate, global_force_quantum;
 	struct spa_list collect;
@@ -1221,7 +1222,8 @@ again:
 		n->runnable = n->always_process && n->active;
 	}
 
-	get_quantums(context, &def_quantum, &min_quantum, &max_quantum, &lim_quantum, &rate_quantum);
+	get_quantums(context, &def_quantum, &min_quantum, &max_quantum, &rate_quantum,
+			&floor_quantum, &ceil_quantum);
 	rates = get_rates(context, &def_rate, &n_rates, &global_force_rate);
 
 	global_force_quantum = rate_quantum == 0;
@@ -1500,7 +1502,7 @@ again:
 			if (latency.denom != 0)
 				target_quantum = (latency.num * current_rate / latency.denom);
 			target_quantum = SPA_CLAMP(target_quantum, node_min_quantum, node_max_quantum);
-			target_quantum = SPA_MIN(target_quantum, lim_quantum);
+			target_quantum = SPA_CLAMP(target_quantum, floor_quantum, ceil_quantum);
 
 			if (settings->clock_power_of_two_quantum && !force_quantum)
 				target_quantum = flp2(target_quantum);

src/pipewire/private.h

@@ -28,8 +28,8 @@ struct ucred {
 #endif
 
 #define MAX_RATES				32u
-#define CLOCK_MIN_QUANTUM			4u
+#define CLOCK_QUANTUM_FLOOR			1u
-#define CLOCK_MAX_QUANTUM			65536u
+#define CLOCK_QUANTUM_LIMIT			65536u
 
 struct settings {
 	uint32_t log_level;
@@ -39,7 +39,8 @@ struct settings {
 	uint32_t clock_quantum;			/* default quantum */
 	uint32_t clock_min_quantum;		/* min quantum */
 	uint32_t clock_max_quantum;		/* max quantum */
-	uint32_t clock_quantum_limit;		/* quantum limit */
+	uint32_t clock_quantum_limit;		/* quantum limit (upper bound) */
+	uint32_t clock_quantum_floor;		/* quantum floor (lower bound) */
 	struct spa_rectangle video_size;
 	struct spa_fraction video_rate;
 	uint32_t link_max_buffers;

src/pipewire/settings.c

@@ -26,6 +26,7 @@
 #define DEFAULT_CLOCK_MIN_QUANTUM		32u
 #define DEFAULT_CLOCK_MAX_QUANTUM		2048u
 #define DEFAULT_CLOCK_QUANTUM_LIMIT		8192u
+#define DEFAULT_CLOCK_QUANTUM_FLOOR		4u
 #define DEFAULT_CLOCK_POWER_OF_TWO_QUANTUM	true
 #define DEFAULT_VIDEO_WIDTH			640
 #define DEFAULT_VIDEO_HEIGHT			480
@@ -212,6 +213,7 @@ void pw_settings_init(struct pw_context *this)
 	d->clock_min_quantum = get_default_int(p, "default.clock.min-quantum", DEFAULT_CLOCK_MIN_QUANTUM);
 	d->clock_max_quantum = get_default_int(p, "default.clock.max-quantum", DEFAULT_CLOCK_MAX_QUANTUM);
 	d->clock_quantum_limit = get_default_int(p, "default.clock.quantum-limit", DEFAULT_CLOCK_QUANTUM_LIMIT);
+	d->clock_quantum_floor = get_default_int(p, "default.clock.quantum-floor", DEFAULT_CLOCK_QUANTUM_FLOOR);
 	d->video_size.width = get_default_int(p, "default.video.width", DEFAULT_VIDEO_WIDTH);
 	d->video_size.height = get_default_int(p, "default.video.height", DEFAULT_VIDEO_HEIGHT);
 	d->video_rate.num = get_default_int(p, "default.video.rate.num", DEFAULT_VIDEO_RATE_NUM);
@@ -228,11 +230,13 @@ void pw_settings_init(struct pw_context *this)
 	d->check_rate = get_default_bool(p, "settings.check-rate", DEFAULT_CHECK_RATE);
 
 	d->clock_quantum_limit = SPA_CLAMP(d->clock_quantum_limit,
-			CLOCK_MIN_QUANTUM, CLOCK_MAX_QUANTUM);
+			CLOCK_QUANTUM_FLOOR, CLOCK_QUANTUM_LIMIT);
+	d->clock_quantum_floor = SPA_CLAMP(d->clock_quantum_floor,
+			CLOCK_QUANTUM_FLOOR, d->clock_quantum_limit);
 	d->clock_max_quantum = SPA_CLAMP(d->clock_max_quantum,
-			CLOCK_MIN_QUANTUM, d->clock_quantum_limit);
+			d->clock_quantum_floor, d->clock_quantum_limit);
 	d->clock_min_quantum = SPA_CLAMP(d->clock_min_quantum,
-			CLOCK_MIN_QUANTUM, d->clock_max_quantum);
+			d->clock_quantum_floor, d->clock_max_quantum);
 	d->clock_quantum = SPA_CLAMP(d->clock_quantum,
 			d->clock_min_quantum, d->clock_max_quantum);
 }