linux-kernel - Re: [PATCH] md: don't delay reboot by 1 second if no MD devices exist

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Date:	Fri, 23 Sep 2011 19:55:36 +1000
From:	NeilBrown <neilb@...e.de>
To:	"Daniel P. Berrange" <berrange@...hat.com>
Cc:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] md: don't delay reboot by 1 second if no MD devices
 exist

On Fri, 23 Sep 2011 10:40:45 +0100 "Daniel P. Berrange" <berrange@...hat.com>
wrote:

> From: "Daniel P. Berrange" <berrange@...hat.com>
> 
> The md_notify_reboot() method includes a call to mdelay(1000),
> to deal with "exotic SCSI devices" which are too volatile on
> reboot. The delay is unconditional. Even if the machine does
> not have any block devices, let alone MD devices, the kernel
> shutdown sequence is slowed down.
> 
> 1 second does not matter much with physical hardware, but with
> certain virtualization use cases any wasted time in the bootup
> & shutdown sequence counts for alot.
> 
> * drivers/md/md.c: md_notify_reboot() - only impose a delay if
>   there was at least one MD device to be stopped during reboot
> 
> Signed-off-by: Daniel P. Berrange <berrange@...hat.com>

queued for next merge window .... or maybe even next -rc if I'm feeling
brave.

Thanks,
NeilBrown


> ---
>  drivers/md/md.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 5404b22..ef7ad8d 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8059,12 +8059,13 @@ static int md_notify_reboot(struct notifier_block *this,
>  {
>  	struct list_head *tmp;
>  	mddev_t *mddev;
> +	int need_delay = 0;
>  
>  	if ((code == SYS_DOWN) || (code == SYS_HALT) || (code == SYS_POWER_OFF)) {
>  
>  		printk(KERN_INFO "md: stopping all md devices.\n");
>  
> -		for_each_mddev(mddev, tmp)
> +		for_each_mddev(mddev, tmp) {
>  			if (mddev_trylock(mddev)) {
>  				/* Force a switch to readonly even array
>  				 * appears to still be in use.  Hence
> @@ -8073,13 +8074,16 @@ static int md_notify_reboot(struct notifier_block *this,
>  				md_set_readonly(mddev, 100);
>  				mddev_unlock(mddev);
>  			}
> +			need_delay = 1;
> +		}
>  		/*
>  		 * certain more exotic SCSI devices are known to be
>  		 * volatile wrt too early system reboots. While the
>  		 * right place to handle this issue is the given
>  		 * driver, we do want to have a safe RAID driver ...
>  		 */
> -		mdelay(1000*1);
> +		if (need_delay)
> +			mdelay(1000*1);
>  	}
>  	return NOTIFY_DONE;
>  }


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