Shaohua Li 4b27e1bb44 cfq-iosched: limit coop preemption ... 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>		2009-11-03 20:25:02 +01:00
..
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