Re: Linux MD Raid Bug(?) w/Kernel sync_speed_min Option

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Tue, 8 May 2007, Neil Brown wrote:

> On Tuesday May 8, jpiszcz@lucidpixels.com wrote:
>> Kernel: 2.6.21.1
>>
>> Here is the bug:
>>
>> md2: RAID1 (works fine)
>> md3: RAID5 (only syncs at the sync_speed_min set by the kernel)
>>
>> If I do not run this command:
>> echo 55000 > /sys/block/md3/md/sync_speed_min
>>
>> I will get 2 megabytes per second check speed for RAID 5.
>
> I can only reproduce this if I set the stripe_cache_size somewhat
> larger than the default of 256 - did you do this?
>
> This code (is_mddev_idle) has always been a bit fragile, particularly
> so since the block layer started account IO when it finished rather
> than when it started.
>
> This patch might help though.  Let me know if it does what you expect.
>
> Thanks,
> NeilBrown
>
>
> Signed-off-by: Neil Brown <neilb@suse.de>
>
> ### Diffstat output
> ./drivers/md/md.c |    2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff .prev/drivers/md/md.c ./drivers/md/md.c
> --- .prev/drivers/md/md.c	2007-05-07 17:47:15.000000000 +1000
> +++ ./drivers/md/md.c	2007-05-08 22:57:51.000000000 +1000
> @@ -5095,7 +5095,7 @@ static int is_mddev_idle(mddev_t *mddev)
> 		 *
> 		 * Note: the following is an unsigned comparison.
> 		 */
> -		if ((curr_events - rdev->last_events + 4096) > 8192) {
> +		if ((long)curr_events - (long)rdev->last_events > 8192) {
> 			rdev->last_events = curr_events;
> 			idle = 0;
> 		}
> -
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> I can only reproduce this if I set the stripe_cache_size somewhat
> larger than the default of 256 - did you do this?
Yes, upon bootup I use:
echo 16384 > /sys/block/md3/md/stripe_cache_size

I have applied this patch and will test it now.

Justin.