blk-throttle.h | Explore in Territory

#ifndef BLK_THROTTLE_H
#define BLK_THROTTLE_H

#include "blk-cgroup-rwstat.h"

/*
 * To implement hierarchical throttling, throtl_grps form a tree and bios
 * are dispatched upwards level by level until they reach the top and get
 * issued.  When dispatching bios from the children and local group at each
 * level, if the bios are dispatched into a single bio_list, there's a risk
 * of a local or child group which can queue many bios at once filling up
 * the list starving others.
 *
 * To avoid such starvation, dispatched bios are queued separately
 * according to where they came from.  When they are again dispatched to
 * the parent, they're popped in round-robin order so that no single source
 * hogs the dispatch window.
 *
 * throtl_qnode is used to keep the queued bios separated by their sources.
 * Bios are queued to throtl_qnode which in turn is queued to
 * throtl_service_queue and then dispatched in round-robin order.
 *
 * It's also used to track the reference counts on blkg's.  A qnode always
 * belongs to a throtl_grp and gets queued on itself or the parent, so
 * incrementing the reference of the associated throtl_grp when a qnode is
 * queued and decrementing when dequeued is enough to keep the whole blkg
 * tree pinned while bios are in flight.
 */
struct throtl_qnode { … };

struct throtl_service_queue { … };

enum tg_state_flags { … };

struct throtl_grp { … };

extern struct blkcg_policy blkcg_policy_throtl;

static inline struct throtl_grp *pd_to_tg(struct blkg_policy_data *pd)
{ … }

static inline struct throtl_grp *blkg_to_tg(struct blkcg_gq *blkg)
{ … }

/*
 * Internal throttling interface
 */
#ifndef CONFIG_BLK_DEV_THROTTLING
static inline void blk_throtl_exit(struct gendisk *disk) { }
static inline bool blk_throtl_bio(struct bio *bio) { return false; }
static inline void blk_throtl_cancel_bios(struct gendisk *disk) { }
#else /* CONFIG_BLK_DEV_THROTTLING */
void blk_throtl_exit(struct gendisk *disk);
bool __blk_throtl_bio(struct bio *bio);
void blk_throtl_cancel_bios(struct gendisk *disk);

static inline bool blk_throtl_activated(struct request_queue *q)
{ … }

static inline bool blk_should_throtl(struct bio *bio)
{ … }

static inline bool blk_throtl_bio(struct bio *bio)
{ … }
#endif /* CONFIG_BLK_DEV_THROTTLING */

#endif
linux/block/blk-throttle.h
