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SubjectRe: deadline unfairness
Date
Hello Jan,

On Sunday 23 March 2008, Jan Engelhardt wrote:
> On Mar 22 2008 12:25, Bernd Schubert wrote:
> > some it seems the deadline scheduler is rather unfair. Below is an
> > example of md-raid6 initialization of md3, md4 and md5. All three
> > md-devices do share the same blockdevices (we have patched md to allow
> > parallel rebuild of shared block devices, since for us the cpu is the
> > bottleneck and not the block device).
>
> Could you share this patch? It would be really intersting for use
> with fast based block devices (flash, ramdisk, and such)!

I already tried to push the patch to Neil, but I guess Neil was to busy to
look at it. The patch below is for 2.6.22, but it applies to 2.6.25-git.


Signed-off-by: Bernd Schubert <bs@q-leap.de>

Index: linux-2.6.22/drivers/md/md.c
===================================================================
--- linux-2.6.22.orig/drivers/md/md.c 2007-12-06 19:51:55.000000000 +0100
+++ linux-2.6.22/drivers/md/md.c 2007-12-07 12:07:47.000000000 +0100
@@ -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(); }

/*
@@ -2843,6 +2845,34 @@ __ATTR(sync_speed_max, S_IRUGO|S_IWUSR,


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)
+{
+ char *e;
+ unsigned long n = simple_strtoul(buf, &e, 10);
+
+ if (!*buf || (*e && *e != '\n') || (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;
@@ -2980,6 +3010,7 @@ 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_suspend_lo.attr,
&md_suspend_hi.attr,
@@ -5199,8 +5230,6 @@ 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)
@@ -5264,8 +5293,9 @@ void md_do_sync(mddev_t *mddev)
ITERATE_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 */
Index: linux-2.6.22/include/linux/raid/md_k.h
===================================================================
--- linux-2.6.22.orig/include/linux/raid/md_k.h 2007-12-06 19:51:55.000000000
+0100
+++ linux-2.6.22/include/linux/raid/md_k.h 2007-12-06 19:52:33.000000000 +0100
@@ -170,6 +170,9 @@ 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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