Commit c27e1efb authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: control: Use xarray for faster lookups 

The control elements are managed in a single linked list and we
traverse the whole list for matching each numid or ctl id per every
inquiry of a control element.  This is OK-ish for a small number of
elements but obviously it doesn't scale.  Especially the matching with
the ctl id takes time because it checks each field of the snd_ctl_id
element, e.g. the name string is matched with strcmp().

This patch adds the hash tables with Xarray for improving the lookup
speed of a control element.  There are two xarray tables added to the
card; one for numid and another for ctl id.  For the numid, we use the
numid as the index, while for the ctl id, we calculate a hash key.

The lookup is done via a single xa_load() execution.  As long as the
given control element is found on the Xarray table, that's fine, we
can give back a quick lookup result.  The problem is when no entry
hits on the table, and for this case, we have a slight optimization.
Namely, the driver checks whether we had a collision on Xarray table,
and do a fallback search (linear lookup of the full entries) only if a
hash key collision happened beforehand.
So, in theory, the inquiry for a non-existing element might take still
time even with this patch in a worst case, but this must be pretty
rare.

The feature is enabled via CONFIG_SND_CTL_FAST_LOOKUP, which is turned
on as default.  For simplicity, the option can be turned off only when
CONFIG_EXPERT is set ("You are expert? Then you manage 1000 knobs").

Link: https://lore.kernel.org/r/20211028130027.18764-1-tiwai@suse.de
Link: https://lore.kernel.org/r/20220609180504.775-1-tiwai@suse.de
Link: https://lore.kernel.org/all/cover.1653813866.git.quic_rbankapu@quicinc.com/
Link: https://lore.kernel.org/r/20220610064537.18660-1-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent b13baccc

include/sound/core.h

+6 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <linux/pm.h>			/* pm_message_t */

#include <linux/stringify.h>

#include <linux/printk.h>

#include <linux/xarray.h>



/* number of supported soundcards */

#ifdef CONFIG_SND_DYNAMIC_MINORS
@@ -103,6 +104,11 @@ struct snd_card { 
	size_t user_ctl_alloc_size;	// current memory allocation by user controls.

	struct list_head controls;	/* all controls for this card */

	struct list_head ctl_files;	/* active control files */

#ifdef CONFIG_SND_CTL_FAST_LOOKUP

	struct xarray ctl_numids;	/* hash table for numids */

	struct xarray ctl_hash;		/* hash table for ctl id matching */

	bool ctl_hash_collision;	/* ctl_hash collision seen? */

#endif



	struct snd_info_entry *proc_root;	/* root for soundcard specific files */

	struct proc_dir_entry *proc_root_link;	/* number link to real id */

sound/core/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -154,6 +154,16 @@ config SND_VERBOSE_PRINTK 


	  You don't need this unless you're debugging ALSA.



config SND_CTL_FAST_LOOKUP

	bool "Fast lookup of control elements" if EXPERT

	default y

	select XARRAY_MULTI

	help

	  This option enables the faster lookup of control elements.

	  It will consume more memory because of the additional Xarray.

	  If you want to choose the memory footprint over the performance

	  inevitably, turn this off.



config SND_DEBUG

	bool "Debug"

	help

sound/core/control.c

+148 −32
Original line number Diff line number Diff line
@@ -364,6 +364,93 @@ static int snd_ctl_find_hole(struct snd_card *card, unsigned int count) 
	return 0;

}



/* check whether the given id is contained in the given kctl */

static bool elem_id_matches(const struct snd_kcontrol *kctl,

			    const struct snd_ctl_elem_id *id)

{

	return kctl->id.iface == id->iface &&

		kctl->id.device == id->device &&

		kctl->id.subdevice == id->subdevice &&

		!strncmp(kctl->id.name, id->name, sizeof(kctl->id.name)) &&

		kctl->id.index <= id->index &&

		kctl->id.index + kctl->count > id->index;

}



#ifdef CONFIG_SND_CTL_FAST_LOOKUP

/* Compute a hash key for the corresponding ctl id

 * It's for the name lookup, hence the numid is excluded.

 * The hash key is bound in LONG_MAX to be used for Xarray key.

 */

#define MULTIPLIER	37

static unsigned long get_ctl_id_hash(const struct snd_ctl_elem_id *id)

{

	unsigned long h;

	const unsigned char *p;



	h = id->iface;

	h = MULTIPLIER * h + id->device;

	h = MULTIPLIER * h + id->subdevice;

	for (p = id->name; *p; p++)

		h = MULTIPLIER * h + *p;

	h = MULTIPLIER * h + id->index;

	h &= LONG_MAX;

	return h;

}



/* add hash entries to numid and ctl xarray tables */

static void add_hash_entries(struct snd_card *card,

			     struct snd_kcontrol *kcontrol)

{

	struct snd_ctl_elem_id id = kcontrol->id;

	int i;



	xa_store_range(&card->ctl_numids, kcontrol->id.numid,

		       kcontrol->id.numid + kcontrol->count - 1,

		       kcontrol, GFP_KERNEL);



	for (i = 0; i < kcontrol->count; i++) {

		id.index = kcontrol->id.index + i;

		if (xa_insert(&card->ctl_hash, get_ctl_id_hash(&id),

			      kcontrol, GFP_KERNEL)) {

			/* skip hash for this entry, noting we had collision */

			card->ctl_hash_collision = true;

			dev_dbg(card->dev, "ctl_hash collision %d:%s:%d\n",

				id.iface, id.name, id.index);

		}

	}

}



/* remove hash entries that have been added */

static void remove_hash_entries(struct snd_card *card,

				struct snd_kcontrol *kcontrol)

{

	struct snd_ctl_elem_id id = kcontrol->id;

	struct snd_kcontrol *matched;

	unsigned long h;

	int i;



	for (i = 0; i < kcontrol->count; i++) {

		xa_erase(&card->ctl_numids, id.numid);

		h = get_ctl_id_hash(&id);

		matched = xa_load(&card->ctl_hash, h);

		if (matched && (matched == kcontrol ||

				elem_id_matches(matched, &id)))

			xa_erase(&card->ctl_hash, h);

		id.index++;

		id.numid++;

	}

}

#else /* CONFIG_SND_CTL_FAST_LOOKUP */

static inline void add_hash_entries(struct snd_card *card,

				    struct snd_kcontrol *kcontrol)

{

}

static inline void remove_hash_entries(struct snd_card *card,

				       struct snd_kcontrol *kcontrol)

{

}

#endif /* CONFIG_SND_CTL_FAST_LOOKUP */



enum snd_ctl_add_mode {

	CTL_ADD_EXCLUSIVE, CTL_REPLACE, CTL_ADD_ON_REPLACE,

};
@@ -408,6 +495,8 @@ static int __snd_ctl_add_replace(struct snd_card *card, 
	kcontrol->id.numid = card->last_numid + 1;

	card->last_numid += kcontrol->count;



	add_hash_entries(card, kcontrol);



	for (idx = 0; idx < kcontrol->count; idx++)

		snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_ADD, kcontrol, idx);
@@ -479,6 +568,26 @@ int snd_ctl_replace(struct snd_card *card, struct snd_kcontrol *kcontrol, 
}

EXPORT_SYMBOL(snd_ctl_replace);



static int __snd_ctl_remove(struct snd_card *card,

			    struct snd_kcontrol *kcontrol,

			    bool remove_hash)

{

	unsigned int idx;



	if (snd_BUG_ON(!card || !kcontrol))

		return -EINVAL;

	list_del(&kcontrol->list);



	if (remove_hash)

		remove_hash_entries(card, kcontrol);



	card->controls_count -= kcontrol->count;

	for (idx = 0; idx < kcontrol->count; idx++)

		snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_REMOVE, kcontrol, idx);

	snd_ctl_free_one(kcontrol);

	return 0;

}



/**

 * snd_ctl_remove - remove the control from the card and release it

 * @card: the card instance
@@ -492,16 +601,7 @@ EXPORT_SYMBOL(snd_ctl_replace); 
 */

int snd_ctl_remove(struct snd_card *card, struct snd_kcontrol *kcontrol)

{

	unsigned int idx;



	if (snd_BUG_ON(!card || !kcontrol))

		return -EINVAL;

	list_del(&kcontrol->list);

	card->controls_count -= kcontrol->count;

	for (idx = 0; idx < kcontrol->count; idx++)

		snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_REMOVE, kcontrol, idx);

	snd_ctl_free_one(kcontrol);

	return 0;

	return __snd_ctl_remove(card, kcontrol, true);

}

EXPORT_SYMBOL(snd_ctl_remove);
@@ -642,14 +742,30 @@ int snd_ctl_rename_id(struct snd_card *card, struct snd_ctl_elem_id *src_id, 
		up_write(&card->controls_rwsem);

		return -ENOENT;

	}

	remove_hash_entries(card, kctl);

	kctl->id = *dst_id;

	kctl->id.numid = card->last_numid + 1;

	card->last_numid += kctl->count;

	add_hash_entries(card, kctl);

	up_write(&card->controls_rwsem);

	return 0;

}

EXPORT_SYMBOL(snd_ctl_rename_id);



#ifndef CONFIG_SND_CTL_FAST_LOOKUP

static struct snd_kcontrol *

snd_ctl_find_numid_slow(struct snd_card *card, unsigned int numid)

{

	struct snd_kcontrol *kctl;



	list_for_each_entry(kctl, &card->controls, list) {

		if (kctl->id.numid <= numid && kctl->id.numid + kctl->count > numid)

			return kctl;

	}

	return NULL;

}

#endif /* !CONFIG_SND_CTL_FAST_LOOKUP */



/**

 * snd_ctl_find_numid - find the control instance with the given number-id

 * @card: the card instance
@@ -665,15 +781,13 @@ EXPORT_SYMBOL(snd_ctl_rename_id); 
 */

struct snd_kcontrol *snd_ctl_find_numid(struct snd_card *card, unsigned int numid)

{

	struct snd_kcontrol *kctl;



	if (snd_BUG_ON(!card || !numid))

		return NULL;

	list_for_each_entry(kctl, &card->controls, list) {

		if (kctl->id.numid <= numid && kctl->id.numid + kctl->count > numid)

			return kctl;

	}

	return NULL;

#ifdef CONFIG_SND_CTL_FAST_LOOKUP

	return xa_load(&card->ctl_numids, numid);

#else

	return snd_ctl_find_numid_slow(card, numid);

#endif

}

EXPORT_SYMBOL(snd_ctl_find_numid);
@@ -699,21 +813,18 @@ struct snd_kcontrol *snd_ctl_find_id(struct snd_card *card, 
		return NULL;

	if (id->numid != 0)

		return snd_ctl_find_numid(card, id->numid);

	list_for_each_entry(kctl, &card->controls, list) {

		if (kctl->id.iface != id->iface)

			continue;

		if (kctl->id.device != id->device)

			continue;

		if (kctl->id.subdevice != id->subdevice)

			continue;

		if (strncmp(kctl->id.name, id->name, sizeof(kctl->id.name)))

			continue;

		if (kctl->id.index > id->index)

			continue;

		if (kctl->id.index + kctl->count <= id->index)

			continue;

#ifdef CONFIG_SND_CTL_FAST_LOOKUP

	kctl = xa_load(&card->ctl_hash, get_ctl_id_hash(id));

	if (kctl && elem_id_matches(kctl, id))

		return kctl;

	}

	if (!card->ctl_hash_collision)

		return NULL; /* we can rely on only hash table */

#endif

	/* no matching in hash table - try all as the last resort */

	list_for_each_entry(kctl, &card->controls, list)

		if (elem_id_matches(kctl, id))

			return kctl;



	return NULL;

}

EXPORT_SYMBOL(snd_ctl_find_id);
@@ -2195,8 +2306,13 @@ static int snd_ctl_dev_free(struct snd_device *device) 
	down_write(&card->controls_rwsem);

	while (!list_empty(&card->controls)) {

		control = snd_kcontrol(card->controls.next);

		snd_ctl_remove(card, control);

		__snd_ctl_remove(card, control, false);

	}



#ifdef CONFIG_SND_CTL_FAST_LOOKUP

	xa_destroy(&card->ctl_numids);

	xa_destroy(&card->ctl_hash);

#endif

	up_write(&card->controls_rwsem);

	put_device(&card->ctl_dev);

	return 0;

sound/core/init.c

+4 −0
Original line number Diff line number Diff line
@@ -310,6 +310,10 @@ static int snd_card_init(struct snd_card *card, struct device *parent, 
	rwlock_init(&card->ctl_files_rwlock);

	INIT_LIST_HEAD(&card->controls);

	INIT_LIST_HEAD(&card->ctl_files);

#ifdef CONFIG_SND_CTL_FAST_LOOKUP

	xa_init(&card->ctl_numids);

	xa_init(&card->ctl_hash);

#endif

	spin_lock_init(&card->files_lock);

	INIT_LIST_HEAD(&card->files_list);

	mutex_init(&card->memory_mutex);