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From: Swen Schillig <swen@vnet.ibm.com>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH] zfcp: add some internal zfcp adapter statistics
Date: Thu, 6 Dec 2007 10:40:34 +0100
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On Monday 26 November 2007 11:23, Swen Schillig wrote:
> On Sunday 25 November 2007 12:16, James Bottomley wrote:
> > 
> > On Wed, 2007-10-31 at 11:33 +0100, Swen Schillig wrote:
> > > From: Swen Schillig <swen@vnet.ibm.com>
> > > 
> > > add some statistics provided by the zFCP adapter to the sysfs
> > > 
> > > The new zFCP adapter statistics provide a variety of information
> > > about the virtual adapter (subchannel). In order to collect this information
> > > the zFCP driver is extended on one side to query the adapter and
> > > on the other side summarize certain values which can then be fetched on demand.
> > > This information is made available via files(attributes) in the sysfs filesystem.
> > > 
> > > The information provided by the new zFCP adapter statistics can be fetched
> > > by reading from the following files in the sysfs filesystem
> > > 
> > >  /sys/class/scsi_host/host<n>/seconds_active
> > >  /sys/class/scsi_host/host<n>/requests
> > >  /sys/class/scsi_host/host<n>/megabytes
> > >  /sys/class/scsi_host/host<n>/utilization
> > 
> > This lot all look like they belong in the FC transport class statistics
> > (some even already exist there).
> 
> They might look alike but they are not the same. The values provided through the FC transport
> class always refer to the physical port whereas the new values here refer to a virtual adapter or subchannel.
> The attributes provided here are all new and not covered or displayed anywhere else !
> 
> > 
> > > These are the statistics on a virtual adapter (subchannel) level.
> > > In addition latency information is provided on a SCSI device level (LUN) which
> > > can be found at the following location
> > > 
> > >  /sys/class/scsi_device/<H:C:T:L>/device/cmd_latency
> > >  /sys/class/scsi_device/<H:C:T:L>/device/read_latency
> > >  /sys/class/scsi_device/<H:C:T:L>/device/write_latency
> > 
> > These look to duplicate to some degree the figures
> > in /sys/block/<dev>/stat.  Isn't the block device the best place to
> > gather these, if they're useful?  Since user latencies should probably
> > include elevator times.
> 
> Actually no, the latencies covered here are channel- and fabric-latencies grouped by scsi-devices
> and not device-, scsi- or block-latencies. In contrast to the stats provided by the block-layer structure,
> tape devices will be covered here as well .
> 
> > 
> > James
> > 
> > 
> > 
> 
> Cheers Swen
> 

James

were my answers, comments sufficient enough to apply my patch
or is there still something missing required ?

Thanks

Cheers Swen
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