Re: PIO disk writes using 100% system time and performing poorly with VIA vt82c686b on kernels 2.2 & 2.4

[John Weber <weber@nyc.rr.com>]

Thomas Ford wrote:

> Heavy disc writes (eg. unzipping linux kernel source) cause the system
> processor usage (as reported by top/xosview) to jump to 100%, making
> the X mouse/audio freeze etc.
> 
> Such problems occur with the drives connected to VIA vt82c686b south
> bridge: the same drives on a mvp3 show no such problems.
> 
> The behaviour is the same on kernels 2.2.17 & 2.4.3 (both hand
> compiled & RedHat's 2.4.2-2 & 2.2.17-14 in case I was doing something
> wrong).
> 
> The problem is easily demonstrated by hdparm -t. The CPU use jumps to
> system 100% as above and all my drives report ~1.9 MB/sec in PIO mode
> which is far lower than PIO on the mvp3 (~10MB/s).
> 
> DMA mode appears to work fine but I am not using it due to publicised
> potential problems.
> 
> Regards,
> 
> Tom Ford
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Can you share a link to the "publicised potential problems" for DMA mode?

I'm running VIA686A using DMA mode and haven't had any problems.
However, the disk isn't operating as efficiently as I thought it would
(hdparm -t reports 16.3 MB/sec even though I'm using an 80w cable
with an ATA100 drive).  I believe that this is due in part to
corrective measures taken by RedHat to fix potential problems with
the VIA chipset; I saw it reported somewhere that the same configuration
will work 20+ MB/sec on distros like Debian).

-- 
  -o) j o h n  e   w e b e r
  / \ aspiring computer scientist & lover of pengiuns
_\_v