[PATCH] cfq-iosched: don't allow aliased requests to starve others
in [Kernel]
|
Prev: wm8727: add a missing return in wm8727_platform_probe
Next: Kbuild: Add option to set -femit-struct-debug-baseonly
From: Jeff Moyer on 14 Jul 2010 11:20 Hi, In running a test case that tries to trip up the kernel's AIO implementation, we ran into a situation where no other I/O to the device under test would be completed. The test program spawned (in this case) 100 threads, each of which performed the following in a loop: open file O_DIRECT queue 1MB of read I/O from file using 16 iocbs close file repeat The program does NOT wait for the I/O to complete. The file length is only 4MB, meaning that you have 25 threads performing I/O on each of the 4 1MB regions. Both deadline and cfq check for aliased requests in the sorted list of I/Os, and when an alias is found, the request in the rb tree is moved to the dispatch list. So, what happens is that, with this workload, only requests from this program are moved to the dispatch list, starving out all other I/O. The attached patch fixes this problem by issuing all expired requests in the aliased request handling code. The reason I opted to issue all expired requsts is because if we only service a single one, I still see really awful interactivity; an ls would take over 5 minutes to complete. With the attached patch, the ls took about 7 seconds to complete. Comments, as always, are welcome. Cheers, Jeff diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 7982b83..0d8d2cd 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -417,6 +417,7 @@ static inline int cfqg_busy_async_queues(struct cfq_data *cfqd, } static void cfq_dispatch_insert(struct request_queue *, struct request *); +static struct request *cfq_check_fifo(struct cfq_queue *cfqq); static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool, struct io_context *, gfp_t); static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *, @@ -1394,10 +1395,22 @@ static void cfq_add_rq_rb(struct request *rq) /* * looks a little odd, but the first insert might return an alias. - * if that happens, put the alias on the dispatch list + * If that happens, put the alias on the dispatch list, but don't + * allow issuing of aliased requests to starve out the queue. */ - while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL) + while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL) { + int fifo_checked = cfq_cfqq_fifo_expire(cfqq); + struct request *__rq; + cfq_dispatch_insert(cfqd->queue, __alias); + cfq_clear_cfqq_fifo_expire(cfqq); + while ((__rq = cfq_check_fifo(cfqq))) { + cfq_dispatch_insert(cfqd->queue, __rq); + cfq_clear_cfqq_fifo_expire(cfqq); + } + if (fifo_checked) + cfq_mark_cfqq_fifo_expire(cfqq); + } if (!cfq_cfqq_on_rr(cfqq)) cfq_add_cfqq_rr(cfqd, cfqq); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |