cfq-iosched: limit coop preemption (4b27e1bb) · Commits · 戴 / test

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>

block/cfq-iosched.c

+15 −2

Original line number	Diff line number	Diff line
		@@ -196,6 +196,7 @@ enum cfqq_state_flags {
		CFQ_CFQQ_FLAG_slice_new, /* no requests dispatched in slice */
		CFQ_CFQQ_FLAG_sync, /* synchronous queue */
		CFQ_CFQQ_FLAG_coop, /* has done a coop jump of the queue */
		CFQ_CFQQ_FLAG_coop_preempt, /* coop preempt */
		};

		#define CFQ_CFQQ_FNS(name) \
		@@ -222,6 +223,7 @@ CFQ_CFQQ_FNS(prio_changed);
		CFQ_CFQQ_FNS(slice_new);
		CFQ_CFQQ_FNS(sync);
		CFQ_CFQQ_FNS(coop);
		CFQ_CFQQ_FNS(coop_preempt);
		#undef CFQ_CFQQ_FNS

		#define cfq_log_cfqq(cfqd, cfqq, fmt, args...) \
		@@ -945,10 +947,13 @@ static struct cfq_queue cfq_set_active_queue(struct cfq_data cfqd,
		{
		if (!cfqq) {
		cfqq = cfq_get_next_queue(cfqd);
		if (cfqq)
		if (cfqq && !cfq_cfqq_coop_preempt(cfqq))
		cfq_clear_cfqq_coop(cfqq);
		}

		if (cfqq)
		cfq_clear_cfqq_coop_preempt(cfqq);

		__cfq_set_active_queue(cfqd, cfqq);
		return cfqq;
		}
		@@ -2066,8 +2071,16 @@ cfq_should_preempt(struct cfq_data cfqd, struct cfq_queue new_cfqq,
		* if this request is as-good as one we would expect from the
		* current cfqq, let it preempt
		*/
		if (cfq_rq_close(cfqd, rq))
		if (cfq_rq_close(cfqd, rq) && (!cfq_cfqq_coop(new_cfqq) \|\|
		cfqd->busy_queues == 1)) {
		/*
		* Mark new queue coop_preempt, so its coop flag will not be
		* cleared when new queue gets scheduled at the very first time
		*/
		cfq_mark_cfqq_coop_preempt(new_cfqq);
		cfq_mark_cfqq_coop(new_cfqq);
		return true;
		}

		return false;
		}

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