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md/raid456: downlevel multicore operations to raid_run_ops

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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: Holger Kiehl <Holger.Kiehl@dwd.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
Dan Williams 2009-10-16 16:25:22 +11:00 committed by NeilBrown
parent dce3a7a42d
commit 417b8d4ac8
2 changed files with 51 additions and 36 deletions
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75
drivers/md/raid5.c
View file

@ -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);

12
drivers/md/raid5.h
View file

@ -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
*/