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Subject[PATCH 009 of 10] md: Allow parallel resync of md-devices.

From: Bernd Schubert <bs@q-leap.de>

In some configurations, a raid6 resync can be limited by CPU speed
(Calculating P and Q and moving data) rather than by device speed.
In these cases there is nothing to be gained byt serialising resync
of arrays that share a device, and doing the resync in parallel can
provide benefit.
So add a sysfs tunable to flag an array as being allowed to
resync in parallel with other arrays that use (a different part of)
the same device.


Signed-off-by: Bernd Schubert <bs@q-leap.de>
Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./drivers/md/md.c | 40 ++++++++++++++++++++++++++++++++++++----
./include/linux/raid/md_k.h | 3 +++
2 files changed, 39 insertions(+), 4 deletions(-)
diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c 2008-05-19 11:03:47.000000000 +1000
+++ ./drivers/md/md.c 2008-05-19 11:04:07.000000000 +1000
@@ -74,6 +74,8 @@ static DEFINE_SPINLOCK(pers_lock);

static void md_print_devices(void);

+static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
+
#define MD_BUG(x...) { printk("md: bug in file %s, line %d\n", __FILE__, __LINE__); md_print_devices(); }

/*
@@ -3013,6 +3015,36 @@ degraded_show(mddev_t *mddev, char *page
static struct md_sysfs_entry md_degraded = __ATTR_RO(degraded);

static ssize_t
+sync_force_parallel_show(mddev_t *mddev, char *page)
+{
+ return sprintf(page, "%d\n", mddev->parallel_resync);
+}
+
+static ssize_t
+sync_force_parallel_store(mddev_t *mddev, const char *buf, size_t len)
+{
+ long n;
+
+ if (strict_strtol(buf, 10, &n))
+ return -EINVAL;
+
+ if (n != 0 && n != 1)
+ return -EINVAL;
+
+ mddev->parallel_resync = n;
+
+ if (mddev->sync_thread)
+ wake_up(&resync_wait);
+
+ return len;
+}
+
+/* force parallel resync, even with shared block devices */
+static struct md_sysfs_entry md_sync_force_parallel =
+__ATTR(sync_force_parallel, S_IRUGO|S_IWUSR,
+ sync_force_parallel_show, sync_force_parallel_store);
+
+static ssize_t
sync_speed_show(mddev_t *mddev, char *page)
{
unsigned long resync, dt, db;
@@ -3187,6 +3219,7 @@ static struct attribute *md_redundancy_a
&md_sync_min.attr,
&md_sync_max.attr,
&md_sync_speed.attr,
+ &md_sync_force_parallel.attr,
&md_sync_completed.attr,
&md_max_sync.attr,
&md_suspend_lo.attr,
@@ -5487,8 +5520,6 @@ void md_allow_write(mddev_t *mddev)
}
EXPORT_SYMBOL_GPL(md_allow_write);

-static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
-
#define SYNC_MARKS 10
#define SYNC_MARK_STEP (3*HZ)
void md_do_sync(mddev_t *mddev)
@@ -5552,8 +5583,9 @@ void md_do_sync(mddev_t *mddev)
for_each_mddev(mddev2, tmp) {
if (mddev2 == mddev)
continue;
- if (mddev2->curr_resync &&
- match_mddev_units(mddev,mddev2)) {
+ if (!mddev->parallel_resync
+ && mddev2->curr_resync
+ && match_mddev_units(mddev, mddev2)) {
DEFINE_WAIT(wq);
if (mddev < mddev2 && mddev->curr_resync == 2) {
/* arbitrarily yield */
diff .prev/include/linux/raid/md_k.h ./include/linux/raid/md_k.h
--- .prev/include/linux/raid/md_k.h 2008-05-19 11:02:06.000000000 +1000
+++ ./include/linux/raid/md_k.h 2008-05-19 11:04:07.000000000 +1000
@@ -180,6 +180,9 @@ struct mddev_s
int sync_speed_min;
int sync_speed_max;

+ /* resync even though the same disks are shared among md-devices */
+ int parallel_resync;
+
int ok_start_degraded;
/* recovery/resync flags
* NEEDED: we might need to start a resync/recover

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