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CFQ has an optimization for cooperated applications. if several io-context have close requests, they will get boost. But the optimization get abused. Considering thread a, b, which work on one file. a reads sectors s, s+2, s+4, ...; b reads sectors s+1, s+3, s +5, ... Both a and b are sequential read, so they can open idle window. a reads a sector s and goes to idle window and wakeup b. b reads sector s+1, since in current implementation, cfq_should_preempt() thinks a and b are cooperators, b will preempt a. b then reads sector s+1 and goes to idle window and wakeup a. for the same reason, a will preempt b and reads s+2. a and b will continue the circle. The circle will be very long, and a and b will occupy whole disk queue. Other applications will nearly have no chance to run. Fix this limiting coop preempt until a queue is scheduled normally again. Signed-off-by: Shaohua Li <shaohua.li@intel.com> Acked-by: Jeff Moyer <jmoyer@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com> |
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.. | ||
as-iosched.c | ||
blk-barrier.c | ||
blk-core.c | ||
blk-exec.c | ||
blk-integrity.c | ||
blk-ioc.c | ||
blk-iopoll.c | ||
blk-map.c | ||
blk-merge.c | ||
blk-settings.c | ||
blk-softirq.c | ||
blk-sysfs.c | ||
blk-tag.c | ||
blk-timeout.c | ||
blk.h | ||
bsg.c | ||
cfq-iosched.c | ||
compat_ioctl.c | ||
deadline-iosched.c | ||
elevator.c | ||
genhd.c | ||
ioctl.c | ||
Kconfig | ||
Kconfig.iosched | ||
Makefile | ||
noop-iosched.c | ||
scsi_ioctl.c |