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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164/* SPDX-License-Identifier: GPL-2.0 *//* * Dynamic queue limits (dql) - Definitions * * Copyright (c) 2011, Tom Herbert <therbert@google.com> * * This header file contains the definitions for dynamic queue limits (dql). * dql would be used in conjunction with a producer/consumer type queue * (possibly a HW queue). Such a queue would have these general properties: * * 1) Objects are queued up to some limit specified as number of objects. * 2) Periodically a completion process executes which retires consumed * objects. * 3) Starvation occurs when limit has been reached, all queued data has * actually been consumed, but completion processing has not yet run * so queuing new data is blocked. * 4) Minimizing the amount of queued data is desirable. * * The goal of dql is to calculate the limit as the minimum number of objects * needed to prevent starvation. * * The primary functions of dql are: * dql_queued - called when objects are enqueued to record number of objects * dql_avail - returns how many objects are available to be queued based * on the object limit and how many objects are already enqueued * dql_completed - called at completion time to indicate how many objects * were retired from the queue * * The dql implementation does not implement any locking for the dql data * structures, the higher layer should provide this. dql_queued should * be serialized to prevent concurrent execution of the function; this * is also true for dql_completed. However, dql_queued and dlq_completed can * be executed concurrently (i.e. they can be protected by different locks). */
#ifndef _LINUX_DQL_H#define _LINUX_DQL_H
#ifdef __KERNEL__
#include <linux/bitops.h>#include <asm/bug.h>
#define DQL_HIST_LEN 4#define DQL_HIST_ENT(dql, idx) ((dql)->history[(idx) % DQL_HIST_LEN])
struct dql { /* Fields accessed in enqueue path (dql_queued) */ unsigned int num_queued; /* Total ever queued */ unsigned int adj_limit; /* limit + num_completed */ unsigned int last_obj_cnt; /* Count at last queuing */
/* Stall threshold (in jiffies), defined by user */ unsigned short stall_thrs;
unsigned long history_head; /* top 58 bits of jiffies */ /* stall entries, a bit per entry */ unsigned long history[DQL_HIST_LEN];
/* Fields accessed only by completion path (dql_completed) */
unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */ unsigned int num_completed; /* Total ever completed */
unsigned int prev_ovlimit; /* Previous over limit */ unsigned int prev_num_queued; /* Previous queue total */ unsigned int prev_last_obj_cnt; /* Previous queuing cnt */
unsigned int lowest_slack; /* Lowest slack found */ unsigned long slack_start_time; /* Time slacks seen */
/* Configuration */ unsigned int max_limit; /* Max limit */ unsigned int min_limit; /* Minimum limit */ unsigned int slack_hold_time; /* Time to measure slack */
/* Longest stall detected, reported to user */ unsigned short stall_max; unsigned long last_reap; /* Last reap (in jiffies) */ unsigned long stall_cnt; /* Number of stalls */};
/* Set some static maximums */#define DQL_MAX_OBJECT (UINT_MAX / 16)#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT)
/* Populate the bitmap to be processed later in dql_check_stall() */static inline void dql_queue_stall(struct dql *dql){ unsigned long map, now, now_hi, i;
now = jiffies; now_hi = now / BITS_PER_LONG;
/* The following code set a bit in the ring buffer, where each * bit trackes time the packet was queued. The dql->history buffer * tracks DQL_HIST_LEN * BITS_PER_LONG time (jiffies) slot */ if (unlikely(now_hi != dql->history_head)) { /* About to reuse slots, clear them */ for (i = 0; i < DQL_HIST_LEN; i++) { /* Multiplication masks high bits */ if (now_hi * BITS_PER_LONG == (dql->history_head + i) * BITS_PER_LONG) break; DQL_HIST_ENT(dql, dql->history_head + i + 1) = 0; } /* pairs with smp_rmb() in dql_check_stall() */ smp_wmb(); WRITE_ONCE(dql->history_head, now_hi); }
/* __set_bit() does not guarantee WRITE_ONCE() semantics */ map = DQL_HIST_ENT(dql, now_hi);
/* Populate the history with an entry (bit) per queued */ if (!(map & BIT_MASK(now))) WRITE_ONCE(DQL_HIST_ENT(dql, now_hi), map | BIT_MASK(now));}
/* * Record number of objects queued. Assumes that caller has already checked * availability in the queue with dql_avail. */static inline void dql_queued(struct dql *dql, unsigned int count){ if (WARN_ON_ONCE(count > DQL_MAX_OBJECT)) return;
WRITE_ONCE(dql->last_obj_cnt, count);
/* We want to force a write first, so that cpu do not attempt * to get cache line containing last_obj_cnt, num_queued, adj_limit * in Shared state, but directly does a Request For Ownership * It is only a hint, we use barrier() only. */ barrier();
dql->num_queued += count;
/* Only populate stall information if the threshold is set */ if (READ_ONCE(dql->stall_thrs)) dql_queue_stall(dql);}
/* Returns how many objects can be queued, < 0 indicates over limit. */static inline int dql_avail(const struct dql *dql){ return READ_ONCE(dql->adj_limit) - READ_ONCE(dql->num_queued);}
/* Record number of completed objects and recalculate the limit. */void dql_completed(struct dql *dql, unsigned int count);
/* Reset dql state */void dql_reset(struct dql *dql);
/* Initialize dql state */void dql_init(struct dql *dql, unsigned int hold_time);
#endif /* _KERNEL_ */
#endif /* _LINUX_DQL_H */