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