Re: NetBSD block vs raw disk I/O

[Sad Clouds <cryintothebluesky%gmail.com@localhost>]

On Fri, 10 Aug 2018 22:01:19 +0200
Jaromír Doleček <jaromir.dolecek%gmail.com@localhost> wrote:

> 2018-08-10 11:35 GMT+02:00 Sad Clouds <cryintothebluesky%gmail.com@localhost>:
> > localhost# dd if=/dev/rsd0d of=/dev/null bs=1m count=10000
> > 10000+0 records in
> > 10000+0 records out
> > 10485760000 bytes transferred in 11.749 secs (892481062 bytes/sec)
> >
> > localhost# dd if=/dev/sd0d of=/dev/null bs=1m count=10000
> > 10000+0 records in
> > 10000+0 records out
> > 10485760000 bytes transferred in 196.552 secs (53348528 bytes/sec)
> >
> > Any ideas why block device I/O is so abysmal? Is this something
> > specific to NetBSD?
> 
> There is some experimental code on -current to optimize one part of
> the read/write-based I/O, supported on amd64.
> 
> You can just boot a -current kernel (for example one from daily
> builds) to single user, and enable the code by escaping to DDB and
> setting variable ubc_direct to 1 (ctrl-alt-esc will give you DDB
> prompt, then 'w ubc_direct 1'), then 'continue' in DDB, then run your
> dd command.
> 
> Jaromir

Thanks, I don't think I'll need it, I just wanted to test how NetBSD
would perform on this disk device, but as was explained to me, real file
system I/O uses a different data path and should be much faster.