Re: SATA Performance with Intel ICH6

[Martin A. Fink]

Am Freitag, 24. November 2006 15:30 schrieben Sie:
> On Fri, 24 Nov 2006 15:10:11 +0100
> "Martin A. Fink" <fink@xxxxxxxxxx> wrote:
> 
> > Well this seems to be independend from the file system. I tried to write 
> > directly to the raw device, but nevertheless the cpu time was 20% (sys 
time).
> 
> sys time is not neccessarily CPU time.
>  
> > This is an interessting point. The specification say that I can handle 
around 
> > 120 to 150 MB/s each of the 4 S-ATA ports. With ICH6 the S-ATA ports seem 
to 
> 
> At once ?
> 
> > be directly connected to the Southbridge, and the Southbridge is directly 
> > connected to Northbridge via PCI Express. So it should be possible to get 
150 
> > MB/s from north to south and from there in packages of 55 MB/s to the 
> > disks ?!
> 
> Ask the vendor.
>  
> > <6>scsi1 : ata_piix
> > <5>  Vendor: ATA       Model: WDC WD740GD-75FL  Rev: 21.0
> > <5>  Type:   Direct-Access                      ANSI SCSI revision: 05
> 
> The PIIX interface needs CPU intervention each command, so in practice
> about every 64K or so, and the CPU gets stalled waiting for the disk
> during the setup of each I/O. The newer kernels support AHCI which does
> not have this overhead, but it is only present on the newest intel
> controllers.

Can you tell me the name of this controllers? Is it ICH7 or 8 ?
What kernel versions?

Thank you very much
> 
> > and strace dd... gives among other information
> > 6.84s 1004calls syscall: write
> > 
> > So I spend 45s of 52s within the kernel. Why so long?
> 
> Waiting for the disk I would imagine.
> 
> Alan
> 
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-- 
Dipl. Physiker
Martin Anton Fink
Max Planck Institute for extraterrestrial Physics
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