linux/block/blk-cgroup.h
Waiman Long 3b8cc62987 blk-cgroup: Optimize blkcg_rstat_flush()
For a system with many CPUs and block devices, the time to do
blkcg_rstat_flush() from cgroup_rstat_flush() can be rather long. It
can be especially problematic as interrupt is disabled during the flush.
It was reported that it might take seconds to complete in some extreme
cases leading to hard lockup messages.

As it is likely that not all the percpu blkg_iostat_set's has been
updated since the last flush, those stale blkg_iostat_set's don't need
to be flushed in this case. This patch optimizes blkcg_rstat_flush()
by keeping a lockless list of recently updated blkg_iostat_set's in a
newly added percpu blkcg->lhead pointer.

The blkg_iostat_set is added to a lockless list on the update side
in blk_cgroup_bio_start(). It is removed from the lockless list when
flushed in blkcg_rstat_flush(). Due to racing, it is possible that
blk_iostat_set's in the lockless list may have no new IO stats to be
flushed, but that is OK.

To protect against destruction of blkg, a percpu reference is gotten
when putting into the lockless list and put back when removed.

When booting up an instrumented test kernel with this patch on a
2-socket 96-thread system with cgroup v2, out of the 2051 calls to
cgroup_rstat_flush() after bootup, 1788 of the calls were exited
immediately because of empty lockless list. After an all-cpu kernel
build, the ratio became 6295424/6340513. That was more than 99%.

Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20221105005902.407297-3-longman@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-11-16 16:58:44 -07:00

521 lines
16 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _BLK_CGROUP_PRIVATE_H
#define _BLK_CGROUP_PRIVATE_H
/*
* block cgroup private header
*
* Based on ideas and code from CFQ, CFS and BFQ:
* Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
*
* Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
* Paolo Valente <paolo.valente@unimore.it>
*
* Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
* Nauman Rafique <nauman@google.com>
*/
#include <linux/blk-cgroup.h>
#include <linux/cgroup.h>
#include <linux/kthread.h>
#include <linux/blk-mq.h>
#include <linux/llist.h>
struct blkcg_gq;
struct blkg_policy_data;
/* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */
#define BLKG_STAT_CPU_BATCH (INT_MAX / 2)
#ifdef CONFIG_BLK_CGROUP
enum blkg_iostat_type {
BLKG_IOSTAT_READ,
BLKG_IOSTAT_WRITE,
BLKG_IOSTAT_DISCARD,
BLKG_IOSTAT_NR,
};
struct blkg_iostat {
u64 bytes[BLKG_IOSTAT_NR];
u64 ios[BLKG_IOSTAT_NR];
};
struct blkg_iostat_set {
struct u64_stats_sync sync;
struct blkcg_gq *blkg;
struct llist_node lnode;
int lqueued; /* queued in llist */
struct blkg_iostat cur;
struct blkg_iostat last;
};
/* association between a blk cgroup and a request queue */
struct blkcg_gq {
/* Pointer to the associated request_queue */
struct request_queue *q;
struct list_head q_node;
struct hlist_node blkcg_node;
struct blkcg *blkcg;
/* all non-root blkcg_gq's are guaranteed to have access to parent */
struct blkcg_gq *parent;
/* reference count */
struct percpu_ref refcnt;
/* is this blkg online? protected by both blkcg and q locks */
bool online;
struct blkg_iostat_set __percpu *iostat_cpu;
struct blkg_iostat_set iostat;
struct blkg_policy_data *pd[BLKCG_MAX_POLS];
spinlock_t async_bio_lock;
struct bio_list async_bios;
union {
struct work_struct async_bio_work;
struct work_struct free_work;
};
atomic_t use_delay;
atomic64_t delay_nsec;
atomic64_t delay_start;
u64 last_delay;
int last_use;
struct rcu_head rcu_head;
};
struct blkcg {
struct cgroup_subsys_state css;
spinlock_t lock;
refcount_t online_pin;
struct radix_tree_root blkg_tree;
struct blkcg_gq __rcu *blkg_hint;
struct hlist_head blkg_list;
struct blkcg_policy_data *cpd[BLKCG_MAX_POLS];
struct list_head all_blkcgs_node;
/*
* List of updated percpu blkg_iostat_set's since the last flush.
*/
struct llist_head __percpu *lhead;
#ifdef CONFIG_BLK_CGROUP_FC_APPID
char fc_app_id[FC_APPID_LEN];
#endif
#ifdef CONFIG_CGROUP_WRITEBACK
struct list_head cgwb_list;
#endif
};
static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
{
return css ? container_of(css, struct blkcg, css) : NULL;
}
/*
* A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
* request_queue (q). This is used by blkcg policies which need to track
* information per blkcg - q pair.
*
* There can be multiple active blkcg policies and each blkg:policy pair is
* represented by a blkg_policy_data which is allocated and freed by each
* policy's pd_alloc/free_fn() methods. A policy can allocate private data
* area by allocating larger data structure which embeds blkg_policy_data
* at the beginning.
*/
struct blkg_policy_data {
/* the blkg and policy id this per-policy data belongs to */
struct blkcg_gq *blkg;
int plid;
};
/*
* Policies that need to keep per-blkcg data which is independent from any
* request_queue associated to it should implement cpd_alloc/free_fn()
* methods. A policy can allocate private data area by allocating larger
* data structure which embeds blkcg_policy_data at the beginning.
* cpd_init() is invoked to let each policy handle per-blkcg data.
*/
struct blkcg_policy_data {
/* the blkcg and policy id this per-policy data belongs to */
struct blkcg *blkcg;
int plid;
};
typedef struct blkcg_policy_data *(blkcg_pol_alloc_cpd_fn)(gfp_t gfp);
typedef void (blkcg_pol_init_cpd_fn)(struct blkcg_policy_data *cpd);
typedef void (blkcg_pol_free_cpd_fn)(struct blkcg_policy_data *cpd);
typedef void (blkcg_pol_bind_cpd_fn)(struct blkcg_policy_data *cpd);
typedef struct blkg_policy_data *(blkcg_pol_alloc_pd_fn)(gfp_t gfp,
struct request_queue *q, struct blkcg *blkcg);
typedef void (blkcg_pol_init_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_online_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_offline_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_free_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd,
struct seq_file *s);
struct blkcg_policy {
int plid;
/* cgroup files for the policy */
struct cftype *dfl_cftypes;
struct cftype *legacy_cftypes;
/* operations */
blkcg_pol_alloc_cpd_fn *cpd_alloc_fn;
blkcg_pol_init_cpd_fn *cpd_init_fn;
blkcg_pol_free_cpd_fn *cpd_free_fn;
blkcg_pol_bind_cpd_fn *cpd_bind_fn;
blkcg_pol_alloc_pd_fn *pd_alloc_fn;
blkcg_pol_init_pd_fn *pd_init_fn;
blkcg_pol_online_pd_fn *pd_online_fn;
blkcg_pol_offline_pd_fn *pd_offline_fn;
blkcg_pol_free_pd_fn *pd_free_fn;
blkcg_pol_reset_pd_stats_fn *pd_reset_stats_fn;
blkcg_pol_stat_pd_fn *pd_stat_fn;
};
extern struct blkcg blkcg_root;
extern bool blkcg_debug_stats;
int blkcg_init_disk(struct gendisk *disk);
void blkcg_exit_disk(struct gendisk *disk);
/* Blkio controller policy registration */
int blkcg_policy_register(struct blkcg_policy *pol);
void blkcg_policy_unregister(struct blkcg_policy *pol);
int blkcg_activate_policy(struct request_queue *q,
const struct blkcg_policy *pol);
void blkcg_deactivate_policy(struct request_queue *q,
const struct blkcg_policy *pol);
const char *blkg_dev_name(struct blkcg_gq *blkg);
void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
u64 (*prfill)(struct seq_file *,
struct blkg_policy_data *, int),
const struct blkcg_policy *pol, int data,
bool show_total);
u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);
struct blkg_conf_ctx {
struct block_device *bdev;
struct blkcg_gq *blkg;
char *body;
};
struct block_device *blkcg_conf_open_bdev(char **inputp);
int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
char *input, struct blkg_conf_ctx *ctx);
void blkg_conf_finish(struct blkg_conf_ctx *ctx);
/**
* bio_issue_as_root_blkg - see if this bio needs to be issued as root blkg
* @return: true if this bio needs to be submitted with the root blkg context.
*
* In order to avoid priority inversions we sometimes need to issue a bio as if
* it were attached to the root blkg, and then backcharge to the actual owning
* blkg. The idea is we do bio_blkcg_css() to look up the actual context for
* the bio and attach the appropriate blkg to the bio. Then we call this helper
* and if it is true run with the root blkg for that queue and then do any
* backcharging to the originating cgroup once the io is complete.
*/
static inline bool bio_issue_as_root_blkg(struct bio *bio)
{
return (bio->bi_opf & (REQ_META | REQ_SWAP)) != 0;
}
/**
* blkg_lookup - lookup blkg for the specified blkcg - q pair
* @blkcg: blkcg of interest
* @q: request_queue of interest
*
* Lookup blkg for the @blkcg - @q pair.
* Must be called in a RCU critical section.
*/
static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
struct request_queue *q)
{
struct blkcg_gq *blkg;
WARN_ON_ONCE(!rcu_read_lock_held());
if (blkcg == &blkcg_root)
return q->root_blkg;
blkg = rcu_dereference(blkcg->blkg_hint);
if (blkg && blkg->q == q)
return blkg;
blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id);
if (blkg && blkg->q != q)
blkg = NULL;
return blkg;
}
/**
* blkg_to_pdata - get policy private data
* @blkg: blkg of interest
* @pol: policy of interest
*
* Return pointer to private data associated with the @blkg-@pol pair.
*/
static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
struct blkcg_policy *pol)
{
return blkg ? blkg->pd[pol->plid] : NULL;
}
static inline struct blkcg_policy_data *blkcg_to_cpd(struct blkcg *blkcg,
struct blkcg_policy *pol)
{
return blkcg ? blkcg->cpd[pol->plid] : NULL;
}
/**
* pdata_to_blkg - get blkg associated with policy private data
* @pd: policy private data of interest
*
* @pd is policy private data. Determine the blkg it's associated with.
*/
static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
{
return pd ? pd->blkg : NULL;
}
static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
{
return cpd ? cpd->blkcg : NULL;
}
/**
* blkg_path - format cgroup path of blkg
* @blkg: blkg of interest
* @buf: target buffer
* @buflen: target buffer length
*
* Format the path of the cgroup of @blkg into @buf.
*/
static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
{
return cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
}
/**
* blkg_get - get a blkg reference
* @blkg: blkg to get
*
* The caller should be holding an existing reference.
*/
static inline void blkg_get(struct blkcg_gq *blkg)
{
percpu_ref_get(&blkg->refcnt);
}
/**
* blkg_tryget - try and get a blkg reference
* @blkg: blkg to get
*
* This is for use when doing an RCU lookup of the blkg. We may be in the midst
* of freeing this blkg, so we can only use it if the refcnt is not zero.
*/
static inline bool blkg_tryget(struct blkcg_gq *blkg)
{
return blkg && percpu_ref_tryget(&blkg->refcnt);
}
/**
* blkg_put - put a blkg reference
* @blkg: blkg to put
*/
static inline void blkg_put(struct blkcg_gq *blkg)
{
percpu_ref_put(&blkg->refcnt);
}
/**
* blkg_for_each_descendant_pre - pre-order walk of a blkg's descendants
* @d_blkg: loop cursor pointing to the current descendant
* @pos_css: used for iteration
* @p_blkg: target blkg to walk descendants of
*
* Walk @c_blkg through the descendants of @p_blkg. Must be used with RCU
* read locked. If called under either blkcg or queue lock, the iteration
* is guaranteed to include all and only online blkgs. The caller may
* update @pos_css by calling css_rightmost_descendant() to skip subtree.
* @p_blkg is included in the iteration and the first node to be visited.
*/
#define blkg_for_each_descendant_pre(d_blkg, pos_css, p_blkg) \
css_for_each_descendant_pre((pos_css), &(p_blkg)->blkcg->css) \
if (((d_blkg) = blkg_lookup(css_to_blkcg(pos_css), \
(p_blkg)->q)))
/**
* blkg_for_each_descendant_post - post-order walk of a blkg's descendants
* @d_blkg: loop cursor pointing to the current descendant
* @pos_css: used for iteration
* @p_blkg: target blkg to walk descendants of
*
* Similar to blkg_for_each_descendant_pre() but performs post-order
* traversal instead. Synchronization rules are the same. @p_blkg is
* included in the iteration and the last node to be visited.
*/
#define blkg_for_each_descendant_post(d_blkg, pos_css, p_blkg) \
css_for_each_descendant_post((pos_css), &(p_blkg)->blkcg->css) \
if (((d_blkg) = blkg_lookup(css_to_blkcg(pos_css), \
(p_blkg)->q)))
bool __blkcg_punt_bio_submit(struct bio *bio);
static inline bool blkcg_punt_bio_submit(struct bio *bio)
{
if (bio->bi_opf & REQ_CGROUP_PUNT)
return __blkcg_punt_bio_submit(bio);
else
return false;
}
static inline void blkcg_bio_issue_init(struct bio *bio)
{
bio_issue_init(&bio->bi_issue, bio_sectors(bio));
}
static inline void blkcg_use_delay(struct blkcg_gq *blkg)
{
if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
return;
if (atomic_add_return(1, &blkg->use_delay) == 1)
atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
}
static inline int blkcg_unuse_delay(struct blkcg_gq *blkg)
{
int old = atomic_read(&blkg->use_delay);
if (WARN_ON_ONCE(old < 0))
return 0;
if (old == 0)
return 0;
/*
* We do this song and dance because we can race with somebody else
* adding or removing delay. If we just did an atomic_dec we'd end up
* negative and we'd already be in trouble. We need to subtract 1 and
* then check to see if we were the last delay so we can drop the
* congestion count on the cgroup.
*/
while (old && !atomic_try_cmpxchg(&blkg->use_delay, &old, old - 1))
;
if (old == 0)
return 0;
if (old == 1)
atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
return 1;
}
/**
* blkcg_set_delay - Enable allocator delay mechanism with the specified delay amount
* @blkg: target blkg
* @delay: delay duration in nsecs
*
* When enabled with this function, the delay is not decayed and must be
* explicitly cleared with blkcg_clear_delay(). Must not be mixed with
* blkcg_[un]use_delay() and blkcg_add_delay() usages.
*/
static inline void blkcg_set_delay(struct blkcg_gq *blkg, u64 delay)
{
int old = atomic_read(&blkg->use_delay);
/* We only want 1 person setting the congestion count for this blkg. */
if (!old && atomic_try_cmpxchg(&blkg->use_delay, &old, -1))
atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
atomic64_set(&blkg->delay_nsec, delay);
}
/**
* blkcg_clear_delay - Disable allocator delay mechanism
* @blkg: target blkg
*
* Disable use_delay mechanism. See blkcg_set_delay().
*/
static inline void blkcg_clear_delay(struct blkcg_gq *blkg)
{
int old = atomic_read(&blkg->use_delay);
/* We only want 1 person clearing the congestion count for this blkg. */
if (old && atomic_try_cmpxchg(&blkg->use_delay, &old, 0))
atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
}
/**
* blk_cgroup_mergeable - Determine whether to allow or disallow merges
* @rq: request to merge into
* @bio: bio to merge
*
* @bio and @rq should belong to the same cgroup and their issue_as_root should
* match. The latter is necessary as we don't want to throttle e.g. a metadata
* update because it happens to be next to a regular IO.
*/
static inline bool blk_cgroup_mergeable(struct request *rq, struct bio *bio)
{
return rq->bio->bi_blkg == bio->bi_blkg &&
bio_issue_as_root_blkg(rq->bio) == bio_issue_as_root_blkg(bio);
}
void blk_cgroup_bio_start(struct bio *bio);
void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta);
#else /* CONFIG_BLK_CGROUP */
struct blkg_policy_data {
};
struct blkcg_policy_data {
};
struct blkcg_policy {
};
struct blkcg {
};
static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }
static inline int blkcg_init_disk(struct gendisk *disk) { return 0; }
static inline void blkcg_exit_disk(struct gendisk *disk) { }
static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
static inline int blkcg_activate_policy(struct request_queue *q,
const struct blkcg_policy *pol) { return 0; }
static inline void blkcg_deactivate_policy(struct request_queue *q,
const struct blkcg_policy *pol) { }
static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
struct blkcg_policy *pol) { return NULL; }
static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }
static inline char *blkg_path(struct blkcg_gq *blkg) { return NULL; }
static inline void blkg_get(struct blkcg_gq *blkg) { }
static inline void blkg_put(struct blkcg_gq *blkg) { }
static inline bool blkcg_punt_bio_submit(struct bio *bio) { return false; }
static inline void blkcg_bio_issue_init(struct bio *bio) { }
static inline void blk_cgroup_bio_start(struct bio *bio) { }
static inline bool blk_cgroup_mergeable(struct request *rq, struct bio *bio) { return true; }
#define blk_queue_for_each_rl(rl, q) \
for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)
#endif /* CONFIG_BLK_CGROUP */
#endif /* _BLK_CGROUP_PRIVATE_H */