Messages in this thread |  | | | Date | Fri, 24 Nov 2006 14:30:40 +0000 | | From | Alan <> | | Subject | Re: SATA Performance with Intel ICH6 |
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On Fri, 24 Nov 2006 15:10:11 +0100 "Martin A. Fink" <fink@mpe.mpg.de> 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.
> 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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