Re: parallel resync

[Neil Brown <neilb@suse.de>]

On Tuesday April 29, bs@q-leap.de wrote:
> Hello Neil,
> 
> I think in about December I already asked if you could include our parallel 
> resync patch. We need this patch, since we are doing software raid over 
> fast hardware raid devices and with these hardware raid system the cpu is 
> the bottleneck and not disk i/o.
> 
> Here is the previous thread: http://www.issociate.de/board/post/470063/[PATCH]_(2nd_try)_force_parallel_resync.html
> 
> Is there any chance you could add this patch as well, or if the patch is 
> not suitable yet, could you please tell me what needs to be done?
> 

Sorry for not responding earlier....

I seem to remember the setting used to be global, but I see in this
patch it is per-array -- which makes much more sense.
Though it brings up an interesting question.  If two arrays share a
device, and exactly one of them is flagged for parallel sync, does
that make sense?

Maybe it does.  I suspect the reality is that it is individual devices
that should be flagged for parallel sync or not, and the setting on
the array is just an "and" of the settings for the devices in the
array.  So different settings on arrays which share one device can
make sense...

Note: I'm *not* suggesting that the setting should be moved to the
component devices - that would be too clumsy.  I'm just musing.

If get 3 errors and 2 warnings from ./scripts/checkpatch.pl.  If you
fix those I'll take the patch.

Thanks,
NeilBrown

ERROR: code indent should use tabs where possible
#85: FILE: drivers/md/md.c:2986:
+        return sprintf(page, "%d\n", mddev->parallel_resync);$

WARNING: consider using strict_strtoul in preference to simple_strtoul
#92: FILE: drivers/md/md.c:2993:
+	unsigned long n = simple_strtoul(buf, &e, 10);

WARNING: braces {} are not necessary for single statement blocks
#99: FILE: drivers/md/md.c:3000:
+	if (mddev->sync_thread) {
+		wake_up(&resync_wait);
+	}

ERROR: space required after that ',' (ctx:VxV)
#139: FILE: drivers/md/md.c:5512:
+			&&  match_mddev_units(mddev,mddev2)) {
 			                           ^

ERROR: Missing Signed-off-by: line(s)

total: 3 errors, 2 warnings, 77 lines checked



> 
> Index: linus/drivers/md/md.c
> ===================================================================
> --- linus.orig/drivers/md/md.c
> +++ linus/drivers/md/md.c
> @@ -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(); }
>  
>  /*
> @@ -2979,6 +2981,34 @@ 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)
> +{
> +	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;
> @@ -3153,6 +3183,7 @@ 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,
> @@ -5413,8 +5444,6 @@ 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)
> @@ -5478,8 +5507,9 @@ 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 */
> Index: linus/include/linux/raid/md_k.h
> ===================================================================
> --- linus.orig/include/linux/raid/md_k.h
> +++ linus/include/linux/raid/md_k.h
> @@ -176,6 +176,9 @@ 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
> 
> 
> 
> Thanks,
> Bernd
> 
> 
> -- 
> Bernd Schubert
> Q-Leap Networks GmbH