Re: 2.6.9 reporting 1 Gigabyte/second throughput on bio's, timer skew possible?

["Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>]

Jens Axboe wrote:

> On Fri, Nov 11 2005, Jeff V. Merkey wrote:
>  
>
> > I have allocated 393,216 bio buffers I statically maintain in a chain 
> > and am running the dsfs file system with 3 x gigabit links fully 
> > saturated.  meta-data
> > increases the write sizes to 720 MB/Second on dual 9500 controllers with 
> > 8 drives each (total of 16) 7200 RPM Drives.  I am seeing some 
> > congestion and bursting on the bio chains as they are submitted.  


> 16 disks on 2 controllers, I'm 100% sure they are lots of people
> pushing 2.6 much further than that! I wouldn't evne call that a big
> setup.
>  
Probably not for this type of application.

>  
>
> > DSFS dynamically generates html status files form within the file 
> > system.  When the system gets somewhat behind, I am seeing bursts > 1 
> > GB/Second which exceeds the theoretical limit of the bus.   I have a 
> > timer function that runs every second and profiles the I/O throughput 
> > created by DSFS with bio submissions and captured packets.  I am asking 
> > if there is clock skew at these data rates with use of the timer 
> > functions.  The system appears to be sustaining 1GB/Second throughput on 
> > dual controllers.  I have verified through data rates the system is 
> > sustaining 800 megabytes/second with these 1GB/S bursts.  I am curious 
> > if there is potentially timer skew at these higher rates since I am 
> > having a hard time accepting that I can push 1GB/S through a bus rated 
> > at only 850 MB/S for DMA based transfers.   The unit is accessible by 
> >    
>
> Note that the linux io stats accounting in 2.6.9 accounts queued io, not
> io completions. So it's quite possible to have burst rates > bus speeds
> for async io. 2.6.15-rc1 change this.
>
>  
So you are willing to log into the unit and validate these numbers? I 
would like for an
someone other than me to validate I am seeing these rates.

Jeff


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