Re: scsi vs ide performance on fsync's

Jeremy Hansen
2001-03-06T16:03:01Z

Ahh, now we're getting somewhere.

IDE:

jeremy:~# time ./xlog file.out fsync

real 0m33.739s
user 0m0.010s
sys 0m0.120s

so now this corresponds to the performance we're seeing on SCSI.

So I guess what I'm wondering now is can or should anything be done about
this on the SCSI side?

Thanks
-jeremy

On Tue, 6 Mar 2001, Mike Black wrote:

> Write caching is the culprit for the performance diff:
>
> On IDE:
> time xlog /blah.dat fsync
> 0.000u 0.190s 0:01.72 11.0% 0+0k 0+0io 91pf+0w
> # hdparm -W 0 /dev/hda
>
> /dev/hda:
> setting drive write-caching to 0 (off)
> # time xlog /blah.dat fsync
> 0.000u 0.220s 0:50.60 0.4% 0+0k 0+0io 91pf+0w
> # hdparm -W 1 /dev/hda
>
> /dev/hda:
> setting drive write-caching to 1 (on)
> # time xlog /blah.dat fsync
> 0.010u 0.230s 0:01.88 12.7% 0+0k 0+0io 91pf+0w
>
> On my SCSI setup:
> # time xlog /usr5/blah.dat fsync
> 0.020u 0.230s 0:30.48 0.8% 0+0k 0+0io 91pf+0w
>
>
> ________________________________________
> Michael D. Black Principal Engineer
> mblack@csihq.com 321-676-2923,x203
> http://www.csihq.com Computer Science Innovations
> http://www.csihq.com/~mike My home page
> FAX 321-676-2355
> ----- Original Message -----
> From: "Andre Hedrick" <andre@linux-ide.org>
> To: "Linus Torvalds" <torvalds@transmeta.com>
> Cc: "Douglas Gilbert" <dougg@torque.net>; <linux-kernel@vger.kernel.org>
> Sent: Tuesday, March 06, 2001 2:12 AM
> Subject: Re: scsi vs ide performance on fsync's
>
>
> On Mon, 5 Mar 2001, Linus Torvalds wrote:
>
> > Well, it's fairly hard for the kernel to do much about that - it's almost
> > certainly just IDE doing write buffering on the disk itself. No OS
> > involved.
>
> I am pushing for WC to be defaulted in the off state, but as you know I
> have a bigger fight than caching on my hands...
>
> > I don't know if there is any way to turn of a write buffer on an IDE disk.
>
> You want a forced set of commands to kill caching at init?
>
> Andre Hedrick
> Linux ATA Development
> ASL Kernel Development
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