RE: Where is the performance bottleneck?

["Guy" <bugzilla@watkins-home.com>]

> -----Original Message-----
> From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
> owner@vger.kernel.org] On Behalf Of Bill Davidsen
> Sent: Wednesday, September 28, 2005 4:05 PM
> To: Guy
> Cc: 'Holger Kiehl'; 'Mark Hahn'; 'linux-raid'; 'linux-kernel'
> Subject: Re: Where is the performance bottleneck?
> 
> Guy wrote:
> 
> >In most of your results, your CPU usage is very high.  Once you get to
> about
> >90% usage, you really can't do much else, unless you can improve the CPU
> >usage.
> >
> That seems one of the problems with software RAID, the calculations are
> done in the CPU and not dedicated hardware. As you move to the top end
> drive hardware the CPU gets to be a limit. I don't remember off the top
> of my head how threaded this code is, and if more CPUs will help.

My old 500MHz P3 can xor at 1GB/sec.  I don't think the RAID5 logic is the
issue!  Also, I have not seen hardware that fast!  Or even half as fast.
But I must admit, I have not seen a hardware RAID5 in a few years.  :(

   8regs     :   918.000 MB/sec
   32regs    :   469.600 MB/sec
   pIII_sse  :   994.800 MB/sec
   pII_mmx   :  1102.400 MB/sec
   p5_mmx    :  1152.800 MB/sec
raid5: using function: pIII_sse (994.800 MB/sec)

Humm..  It did not select the fastest?

Guy
> 
> I see you are using RAID-1 for your system stuff, did one of the tests
> use RAID-0 over all the drives? Mirroring or XOR redundancy help
> stability but hurt performance. Was the 270MB/s with RAID-0 or ???
> 
> --
> bill davidsen <davidsen@tmr.com>
>   CTO TMR Associates, Inc
>   Doing interesting things with small computers since 1979
> 
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