Commit 5bf14c07 authored by Committed by Jens Axboe
block: Make cfq_target_latency tunable through sysfs.
In cfq, when we calculate a time slice for a process(or a cfqq to be precise), we have to consider the cfq_target_latency so that all the sync request have an estimated latency(300ms) and it is controlled by cfq_target_latency. But in some hadoop test, we have found that if there are many processes doing sequential read(24 for example), the throughput is bad because every process can only work for about 25ms and the cfqq is switched. That leads to a higher disk seek. We can achive the good throughput by setting low_latency=0, but then some read's latency is too much for the application. So this patch makes cfq_target_latency tunable through sysfs so that we can tune it and find some magic number which is not bad for both the throughput and the read latency. Cc: Jens Axboe <firstname.lastname@example.org> Signed-off-by: Tao Ma <email@example.com> Signed-off-by: Jens Axboe <firstname.lastname@example.org>
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