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Commit 417b8d4a authored by Dan Williams's avatar Dan Williams Committed by NeilBrown
Browse files

md/raid456: downlevel multicore operations to raid_run_ops 



The percpu conversion allowed a straightforward handoff of stripe
processing to the async subsytem that initially showed some modest gains
(+4%).  However, this model is too simplistic and leads to stripes
bouncing between raid5d and the async thread pool for every invocation
of handle_stripe().  As reported by Holger this can fall into a
pathological situation severely impacting throughput (6x performance
loss).

By downleveling the parallelism to raid_run_ops the pathological
stripe_head bouncing is eliminated.  This version still exhibits an
average 11% throughput loss for:

	mdadm --create /dev/md0 /dev/sd[b-q] -n 16 -l 6
	echo 1024 > /sys/block/md0/md/stripe_cache_size
	dd if=/dev/zero of=/dev/md0 bs=1024k count=2048

...but the results are at least stable and can be used as a base for
further multicore experimentation.

Reported-by: default avatarHolger Kiehl <Holger.Kiehl@dwd.de>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent dce3a7a4

drivers/md/raid5.c

+40 −35
Original line number Diff line number Diff line
@@ -1139,7 +1139,7 @@ static void ops_run_check_pq(struct stripe_head *sh, struct raid5_percpu *percpu 
			   &sh->ops.zero_sum_result, percpu->spare_page, &submit);

}



static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)

static void __raid_run_ops(struct stripe_head *sh, unsigned long ops_request)

{

	int overlap_clear = 0, i, disks = sh->disks;

	struct dma_async_tx_descriptor *tx = NULL;
@@ -1204,6 +1204,36 @@ static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request) 
	put_cpu();

}



#ifdef CONFIG_MULTICORE_RAID456

static void async_run_ops(void *param, async_cookie_t cookie)

{

	struct stripe_head *sh = param;

	unsigned long ops_request = sh->ops.request;



	clear_bit_unlock(STRIPE_OPS_REQ_PENDING, &sh->state);

	wake_up(&sh->ops.wait_for_ops);



	__raid_run_ops(sh, ops_request);

	release_stripe(sh);

}



static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)

{

	/* since handle_stripe can be called outside of raid5d context

	 * we need to ensure sh->ops.request is de-staged before another

	 * request arrives

	 */

	wait_event(sh->ops.wait_for_ops,

		   !test_and_set_bit_lock(STRIPE_OPS_REQ_PENDING, &sh->state));

	sh->ops.request = ops_request;



	atomic_inc(&sh->count);

	async_schedule(async_run_ops, sh);

}

#else

#define raid_run_ops __raid_run_ops

#endif



static int grow_one_stripe(raid5_conf_t *conf)

{

	struct stripe_head *sh;
@@ -1213,6 +1243,9 @@ static int grow_one_stripe(raid5_conf_t *conf) 
	memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));

	sh->raid_conf = conf;

	spin_lock_init(&sh->lock);

	#ifdef CONFIG_MULTICORE_RAID456

	init_waitqueue_head(&sh->ops.wait_for_ops);

	#endif



	if (grow_buffers(sh, conf->raid_disks)) {

		shrink_buffers(sh, conf->raid_disks);
@@ -1329,6 +1362,9 @@ static int resize_stripes(raid5_conf_t *conf, int newsize) 


		nsh->raid_conf = conf;

		spin_lock_init(&nsh->lock);

		#ifdef CONFIG_MULTICORE_RAID456

		init_waitqueue_head(&nsh->ops.wait_for_ops);

		#endif



		list_add(&nsh->lru, &newstripes);

	}
@@ -4342,37 +4378,6 @@ static int retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio) 
	return handled;

}



#ifdef CONFIG_MULTICORE_RAID456

static void __process_stripe(void *param, async_cookie_t cookie)

{

	struct stripe_head *sh = param;



	handle_stripe(sh);

	release_stripe(sh);

}



static void process_stripe(struct stripe_head *sh, struct list_head *domain)

{

	async_schedule_domain(__process_stripe, sh, domain);

}



static void synchronize_stripe_processing(struct list_head *domain)

{

	async_synchronize_full_domain(domain);

}

#else

static void process_stripe(struct stripe_head *sh, struct list_head *domain)

{

	handle_stripe(sh);

	release_stripe(sh);

	cond_resched();

}



static void synchronize_stripe_processing(struct list_head *domain)

{

}

#endif





/*

 * This is our raid5 kernel thread.
@@ -4386,7 +4391,6 @@ static void raid5d(mddev_t *mddev) 
	struct stripe_head *sh;

	raid5_conf_t *conf = mddev->private;

	int handled;

	LIST_HEAD(raid_domain);



	pr_debug("+++ raid5d active\n");
@@ -4423,7 +4427,9 @@ static void raid5d(mddev_t *mddev) 
		spin_unlock_irq(&conf->device_lock);

		

		handled++;

		process_stripe(sh, &raid_domain);

		handle_stripe(sh);

		release_stripe(sh);

		cond_resched();



		spin_lock_irq(&conf->device_lock);

	}
@@ -4431,7 +4437,6 @@ static void raid5d(mddev_t *mddev) 


	spin_unlock_irq(&conf->device_lock);



	synchronize_stripe_processing(&raid_domain);

	async_tx_issue_pending_all();

	unplug_slaves(mddev);

drivers/md/raid5.h

+11 −1
Original line number Diff line number Diff line
@@ -214,12 +214,20 @@ struct stripe_head { 
	int			disks;		/* disks in stripe */

	enum check_states	check_state;

	enum reconstruct_states reconstruct_state;

	/* stripe_operations

	/**

	 * struct stripe_operations

	 * @target - STRIPE_OP_COMPUTE_BLK target

	 * @target2 - 2nd compute target in the raid6 case

	 * @zero_sum_result - P and Q verification flags

	 * @request - async service request flags for raid_run_ops

	 */

	struct stripe_operations {

		int 		     target, target2;

		enum sum_check_flags zero_sum_result;

		#ifdef CONFIG_MULTICORE_RAID456

		unsigned long	     request;

		wait_queue_head_t    wait_for_ops;

		#endif

	} ops;

	struct r5dev {

		struct bio	req;
@@ -294,6 +302,8 @@ struct r6_state { 
#define	STRIPE_FULL_WRITE	13 /* all blocks are set to be overwritten */

#define	STRIPE_BIOFILL_RUN	14

#define	STRIPE_COMPUTE_RUN	15

#define	STRIPE_OPS_REQ_PENDING	16



/*

 * Operation request flags

 */