> Hi,
>
> since using work queues involve more context switches than doing things
> inline... have you measured the performance impact of your changes? If
> so... was there any impact that you could measure, and how big was that?
>
> Greetings,
> Arjan van de Ven
Good point. Especially on ARM extra context switching can be very
expensive. In general more testing (and testers for that matter) is
needed. To facilitate the determination of whether a multi-threaded
work queue is better/worse than an in context implementation here is a
patch that makes this configurable.
Thanks,
Dan
[PATCH] raid5: Configuration options to allow raid ops to run in raid5d context
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
drivers/md/Kconfig | 21 +++++++++++++++++++++
drivers/md/raid5.c | 25 +++++++++++++++++++++++++
include/linux/raid/raid5.h | 6 ++++++
3 files changed, 52 insertions(+)
Index: linux-2.6-raid/drivers/md/Kconfig
===================================================================
--- linux-2.6-raid.orig/drivers/md/Kconfig 2006-06-29 11:40:02.000000000 -0700
+++ linux-2.6-raid/drivers/md/Kconfig 2006-06-29 13:43:03.000000000 -0700
@@ -162,6 +162,27 @@
There should be enough spares already present to make the new
array workable.
+config MD_RAID456_WORKQUEUE
+ depends on MD_RAID456
+ bool "Offload raid work to a workqueue from raid5d"
+ ---help---
+ This option enables raid work (block copy and xor operations)
+ to run in a workqueue. However this may come at the expense of
+ extra context switching. Single processor systems may benefit
+ from keeping the work within the raid5d context.
+
+ If unsure say, Y.
+
+config MD_RAID456_WORKQUEUE_MULTITHREAD
+ depends on MD_RAID456_WORKQUEUE && SMP
+ bool "Enable multi-threaded raid processing"
+ default y
+ ---help---
+ This option controls whether the raid workqueue will be multi-
+ threaded or single threaded.
+
+ If unsure say, Y.
+
config MD_MULTIPATH
tristate "Multipath I/O support"
depends on BLK_DEV_MD
Index: linux-2.6-raid/drivers/md/raid5.c
===================================================================
--- linux-2.6-raid.orig/drivers/md/raid5.c 2006-06-29 13:42:57.000000000 -0700
+++ linux-2.6-raid/drivers/md/raid5.c 2006-06-29 13:43:03.000000000 -0700
@@ -305,7 +305,9 @@
memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
sh->raid_conf = conf;
spin_lock_init(&sh->lock);
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
INIT_WORK(&sh->ops.work, conf->do_block_ops, sh);
+ #endif
if (grow_buffers(sh, conf->raid_disks)) {
shrink_buffers(sh, conf->raid_disks);
@@ -1352,8 +1354,10 @@
{
if (!test_bit(STRIPE_OP_QUEUED, &sh->state) && sh->ops.pending) {
set_bit(STRIPE_OP_QUEUED, &sh->state);
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
atomic_inc(&sh->count);
queue_work(sh->raid_conf->block_ops_queue, &sh->ops.work);
+ #endif
}
}
@@ -1614,7 +1618,9 @@
queue_raid_work(sh);
spin_unlock(&sh->lock);
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
release_stripe(sh);
+ #endif
}
/*
@@ -2182,6 +2188,13 @@
spin_unlock(&sh->lock);
+ #ifndef CONFIG_MD_RAID456_WORKQUEUE
+ while (test_bit(STRIPE_OP_QUEUED, &sh->state)) {
+ PRINTK("run do_block_ops\n", __FUNCTION__);
+ conf->do_block_ops(sh);
+ }
+ #endif
+
while ((bi=return_bi)) {
int bytes = bi->bi_size;
@@ -3480,12 +3493,20 @@
goto abort;
}
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
sprintf(conf->workqueue_name, "%s_raid5_ops",
mddev->gendisk->disk_name);
+ #ifdef CONFIG_MD_RAID456_MULTITHREAD
if ((conf->block_ops_queue = create_workqueue(conf->workqueue_name))
== NULL)
goto abort;
+ #else
+ if ((conf->block_ops_queue = __create_workqueue(conf->workqueue_name, 1))
+ == NULL)
+ goto abort;
+ #endif
+ #endif
/* To Do:
* 1/ Offload to asynchronous copy / xor engines
@@ -3656,8 +3677,10 @@
safe_put_page(conf->spare_page);
kfree(conf->disks);
kfree(conf->stripe_hashtbl);
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
if (conf->do_block_ops)
destroy_workqueue(conf->block_ops_queue);
+ #endif
kfree(conf);
}
mddev->private = NULL;
@@ -3678,7 +3701,9 @@
blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
sysfs_remove_group(&mddev->kobj, &raid5_attrs_group);
kfree(conf->disks);
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
destroy_workqueue(conf->block_ops_queue);
+ #endif
kfree(conf);
mddev->private = NULL;
return 0;
Index: linux-2.6-raid/include/linux/raid/raid5.h
===================================================================
--- linux-2.6-raid.orig/include/linux/raid/raid5.h 2006-06-29 11:53:35.000000000 -0700
+++ linux-2.6-raid/include/linux/raid/raid5.h 2006-06-29 13:43:03.000000000 -0700
@@ -149,7 +149,9 @@
struct stripe_operations {
int pending; /* number of operations requested */
unsigned long state; /* state of block operations */
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
struct work_struct work; /* work queue descriptor */
+ #endif
#ifdef CONFIG_DMA_ENGINE
u32 dma_result; /* storage for dma engine results */
dma_cookie_t dma_cookie; /* last issued dma operation */
@@ -298,7 +300,9 @@
atomic_t reshape_stripes; /* stripes with pending writes for reshape */
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
struct workqueue_struct *block_ops_queue;
+ #endif
void (*do_block_ops)(void *);
/* unfortunately we need two cache names as we temporarily have
@@ -306,7 +310,9 @@
*/
int active_name;
char cache_name[2][20];
+ #ifdef CONFIG_MD_RAID456_WORKQUEUE
char workqueue_name[20];
+ #endif
kmem_cache_t *slab_cache; /* for allocating stripes */
int seq_flush, seq_write;
-
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