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

[jmerkey]

Jens Axboe wrote:

> On Sat, Nov 12 2005, Jeff V. Merkey wrote:
>  
>
> > 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.
> >    
>
> If you average the bandwidth over a time long enough to eliminate the
> bursty queueing rates, your average rage should drop to what the
> hardware can actually do. Or dig out the patch from 2.6.15-rc1 for
> ll_rw_blk.c and apply it to 2.6.9, find it here:
>
> http://kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=d72d904a5367ad4ca3f2c9a2ce8c3a68f0b28bf0;hp=d83c671fb7023f69a9582e622d01525054f23b66
>
>  
Jens,

Thanks. I'll dig out the patch. I am measuring the rates on the back end 
and they are running at 720-800 MB/S apart from what's being reported from
the bio submission. At any rate, I ave to say the bio performance is 
stunning in comparison to Windows 2003.

Jeff
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