md/raid456: distribute raid processing over multiple cores

Now that the resources to handle stripe_head operations are allocated
percpu it is possible for raid5d to distribute stripe handling over
multiple cores.  This conversion also adds a call to cond_resched() in
the non-multicore case to prevent one core from getting monopolized for
raid operations.

Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

2 files changed, 45 insertions, 2 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index abb8636bfde2..09c0c6e49ab5 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -154,6 +154,17 @@ config MD_RAID456
 
           If unsure, say Y.
 
+config MULTICORE_RAID456
+        bool "RAID-4/RAID-5/RAID-6 Multicore processing (EXPERIMENTAL)"
+        depends on MD_RAID456
+        depends on SMP
+        depends on EXPERIMENTAL
+        ---help---
+          Enable the raid456 module to dispatch per-stripe raid operations to a
+          thread pool.
+
+          If unsure, say N.
+
 config MD_RAID6_PQ
         tristate
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7c22e19aca82..364ea37706fa 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -47,6 +47,7 @@
 #include <linux/kthread.h>
 #include <linux/raid/pq.h>
 #include <linux/async_tx.h>
+#include <linux/async.h>
 #include <linux/seq_file.h>
 #include <linux/cpu.h>
 #include "md.h"
@@ -4314,6 +4315,36 @@ 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
 
 
 /*
@@ -4328,6 +4359,7 @@ static void raid5d(mddev_t *mddev)
         struct stripe_head *sh;
         raid5_conf_t *conf = mddev_to_conf(mddev);
         int handled;
+        LIST_HEAD(raid_domain);
 
         pr_debug("+++ raid5d active\n");
 
@@ -4364,8 +4396,7 @@ static void raid5d(mddev_t *mddev)
                 spin_unlock_irq(&conf->device_lock);
                 
                 handled++;
-                handle_stripe(sh);
-                release_stripe(sh);
+                process_stripe(sh, &raid_domain);
 
                 spin_lock_irq(&conf->device_lock);
         }
@@ -4373,6 +4404,7 @@ 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);