linux-kernel - Re: [PATCH 31/40] libata: take advantage of cmwq and remove concurrency limitations

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Message-ID: <4B5482D3.305@s5r6.in-berlin.de>
Date:	Mon, 18 Jan 2010 16:48:35 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Tejun Heo <tj@...nel.org>
CC:	torvalds@...ux-foundation.org, mingo@...e.hu, peterz@...radead.org,
	awalls@...ix.net, linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org,
	Jeff Garzik <jgarzik@...ox.com>
Subject: Re: [PATCH 31/40] libata: take advantage of cmwq and remove concurrency
 limitations

Tejun Heo wrote:
[...]
> b. ata_aux_wq which is used for SCSI probing has single thread.  In
>    cases where SCSI probing is stalled for extended period of time
>    which is possible for ATAPI devices, this will stall all probing.

Are things like INQUIRY and possibly motor spin-up performed there?
If yes, ...

[...]
> #b is solved by using the default wq instead and achieving exclusion
> via per-port mutex.
[...]
> --- a/drivers/ata/libata-eh.c
> +++ b/drivers/ata/libata-eh.c
> @@ -727,7 +727,7 @@ void ata_scsi_error(struct Scsi_Host *host)
>  	if (ap->pflags & ATA_PFLAG_LOADING)
>  		ap->pflags &= ~ATA_PFLAG_LOADING;
>  	else if (ap->pflags & ATA_PFLAG_SCSI_HOTPLUG)
> -		queue_delayed_work(ata_aux_wq, &ap->hotplug_task, 0);
> +		schedule_delayed_work(&ap->hotplug_task, 0);
>  
>  	if (ap->pflags & ATA_PFLAG_RECOVERED)
>  		ata_port_printk(ap, KERN_INFO, "EH complete\n");
> @@ -2938,7 +2938,7 @@ static int ata_eh_revalidate_and_attach(struct ata_link *link,
>  			ehc->i.flags |= ATA_EHI_SETMODE;
>  
>  			/* schedule the scsi_rescan_device() here */
> -			queue_work(ata_aux_wq, &(ap->scsi_rescan_task));
> +			schedule_work(&(ap->scsi_rescan_task));
>  		} else if (dev->class == ATA_DEV_UNKNOWN &&
>  			   ehc->tries[dev->devno] &&
>  			   ata_class_enabled(ehc->classes[dev->devno])) {
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index f4ea5a8..08e2ef8 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -3408,8 +3408,7 @@ void ata_scsi_scan_host(struct ata_port *ap, int sync)
>  				"                  switching to async\n");
>  	}
>  
> -	queue_delayed_work(ata_aux_wq, &ap->hotplug_task,
> -			   round_jiffies_relative(HZ));
> +	schedule_delayed_work(&ap->hotplug_task, round_jiffies_relative(HZ));
>  }
>  
>  /**
[...]

... wouldn't queue_delayed_work(system_long_wq, &ap->hotplug_task, ...);
be more appropriate then?
-- 
Stefan Richter
-=====-==-=- ---= =--=-
http://arcgraph.de/sr/
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