block cfq: make queue preempt work for queues from different workload
I got this: fio-874 [007] 2157.724514: 8,32 m N cfq874 preempt fio-874 [007] 2157.724519: 8,32 m N cfq830 slice expired t=1 fio-874 [007] 2157.724520: 8,32 m N cfq830 sl_used=1 disp=0 charge=1 iops=0 sect=0 fio-874 [007] 2157.724521: 8,32 m N cfq830 set_active wl_prio:0 wl_type:0 fio-874 [007] 2157.724522: 8,32 m N cfq830 Not idling. st->count:1 cfq830 is an async queue, and preempted by a sync queue cfq874. But since we have cfqg->saved_workload_slice mechanism, the preempt is a nop. Looks currently our preempt is totally broken if the two queues are not from the same workload type. Below patch fixes it. This will might make async queue starvation, but it's what our old code does before cgroup is added. Signed-off-by: NShaohua Li <shaohua.li@intel.com> Signed-off-by: NJens Axboe <jaxboe@fusionio.com>
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