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authorPaolo Valente <paolo.valente@linaro.org>2018-08-16 18:51:17 +0200
committerJens Axboe <axboe@kernel.dk>2018-08-16 13:08:13 -0600
commitd5801088a7bd210dd8fd7add04745e35f0f6ea72 (patch)
treea91daecab3318589a0f19f84602fcbb5a779b642 /block/bfq-wf2q.c
parente02a0aa26bf61b6e481a3d7453a150e692b0df80 (diff)
block, bfq: reduce write overcharge
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 an overcharge factor. 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. On the opposite end, 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. The fixes "block, bfq: always update the budget of an entity when needed" and "block, bfq: readd missing reset of parent-entity service" improved I/O control in bfq to such an extent that it has been possible to revise this overcharge factor downwards. This commit introduces the resulting, new value. Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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