diff options
| -rw-r--r-- | block/bfq-iosched.c | 33 |
1 files changed, 19 insertions, 14 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 62efc1b97afb..653100fb719e 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -187,11 +187,25 @@ static const int bfq_stats_min_budgets = 194; static const int bfq_default_max_budget = 16 * 1024; /* - * Async to sync throughput distribution is controlled as follows: - * when an async request is served, the entity is charged the number - * of sectors of the request, multiplied by the factor below + * When a sync request is dispatched, the queue that contains that + * request, and all the ancestor entities of that queue, are charged + * with the number of sectors of the request. In constrast, if the + * request is async, then the queue and its ancestor entities are + * charged with the number of sectors of the request, multiplied by + * the factor below. This throttles the bandwidth for async I/O, + * w.r.t. to sync I/O, and it is done to counter the tendency of async + * writes to steal I/O throughput to reads. + * + * The current value of this parameter is the result of a tuning with + * several hardware and software configurations. We tried to find the + * lowest value for which writes do not cause noticeable problems to + * reads. In fact, the lower this parameter, the stabler I/O control, + * in the following respect. The lower this parameter is, the less + * the bandwidth enjoyed by a group decreases + * - when the group does writes, w.r.t. to when it does reads; + * - when other groups do reads, w.r.t. to when they do writes. */ -static const int bfq_async_charge_factor = 10; +static const int bfq_async_charge_factor = 3; /* Default timeout values, in jiffies, approximating CFQ defaults. */ const int bfq_timeout = HZ / 8; @@ -853,16 +867,7 @@ static unsigned long bfq_serv_to_charge(struct request *rq, if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1) return blk_rq_sectors(rq); - /* - * If there are no weight-raised queues, then amplify service - * by just the async charge factor; otherwise amplify service - * by twice the async charge factor, to further reduce latency - * for weight-raised queues. - */ - if (bfqq->bfqd->wr_busy_queues == 0) - return blk_rq_sectors(rq) * bfq_async_charge_factor; - - return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor; + return blk_rq_sectors(rq) * bfq_async_charge_factor; } /** |