diff options
| -rw-r--r-- | drivers/md/bcache/request.c | 15 | ||||
| -rw-r--r-- | drivers/md/bcache/request.h | 2 | ||||
| -rw-r--r-- | drivers/md/bcache/util.h | 26 |
3 files changed, 28 insertions, 15 deletions
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index f11123079fe0..41adcd1546f1 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -329,12 +329,13 @@ void bch_data_insert(struct closure *cl) bch_data_insert_start(cl); } -/* Congested? */ - -unsigned int bch_get_congested(struct cache_set *c) +/* + * Congested? Return 0 (not congested) or the limit (in sectors) + * beyond which we should bypass the cache due to congestion. + */ +unsigned int bch_get_congested(const struct cache_set *c) { int i; - long rand; if (!c->congested_read_threshold_us && !c->congested_write_threshold_us) @@ -353,8 +354,7 @@ unsigned int bch_get_congested(struct cache_set *c) if (i > 0) i = fract_exp_two(i, 6); - rand = get_random_int(); - i -= bitmap_weight(&rand, BITS_PER_LONG); + i -= hweight32(get_random_u32()); return i > 0 ? i : 1; } @@ -376,7 +376,7 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio) { struct cache_set *c = dc->disk.c; unsigned int mode = cache_mode(dc); - unsigned int sectors, congested = bch_get_congested(c); + unsigned int sectors, congested; struct task_struct *task = current; struct io *i; @@ -412,6 +412,7 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio) goto rescale; } + congested = bch_get_congested(c); if (!congested && !dc->sequential_cutoff) goto rescale; diff --git a/drivers/md/bcache/request.h b/drivers/md/bcache/request.h index 721bf336ed1a..c64dbd7a91aa 100644 --- a/drivers/md/bcache/request.h +++ b/drivers/md/bcache/request.h @@ -33,7 +33,7 @@ struct data_insert_op { BKEY_PADDED(replace_key); }; -unsigned int bch_get_congested(struct cache_set *c); +unsigned int bch_get_congested(const struct cache_set *c); void bch_data_insert(struct closure *cl); void bch_cached_dev_request_init(struct cached_dev *dc); diff --git a/drivers/md/bcache/util.h b/drivers/md/bcache/util.h index 00aab6abcfe4..1fbced94e4cc 100644 --- a/drivers/md/bcache/util.h +++ b/drivers/md/bcache/util.h @@ -560,17 +560,29 @@ static inline uint64_t bch_crc64_update(uint64_t crc, return crc; } -/* Does linear interpolation between powers of two */ +/* + * A stepwise-linear pseudo-exponential. This returns 1 << (x >> + * frac_bits), with the less-significant bits filled in by linear + * interpolation. + * + * This can also be interpreted as a floating-point number format, + * where the low frac_bits are the mantissa (with implicit leading + * 1 bit), and the more significant bits are the exponent. + * The return value is 1.mantissa * 2^exponent. + * + * The way this is used, fract_bits is 6 and the largest possible + * input is CONGESTED_MAX-1 = 1023 (exponent 16, mantissa 0x1.fc), + * so the maximum output is 0x1fc00. + */ static inline unsigned int fract_exp_two(unsigned int x, unsigned int fract_bits) { - unsigned int fract = x & ~(~0 << fract_bits); - - x >>= fract_bits; - x = 1 << x; - x += (x * fract) >> fract_bits; + unsigned int mantissa = 1 << fract_bits; /* Implicit bit */ - return x; + mantissa += x & (mantissa - 1); + x >>= fract_bits; /* The exponent */ + /* Largest intermediate value 0x7f0000 */ + return mantissa << x >> fract_bits; } void bch_bio_map(struct bio *bio, void *base); |