Re: high load, no bottleneck

[Greg Oster <oster%cs.usask.ca@localhost>]

On Thu, 19 Sep 2013 10:29:55 -0400
christos%zoulas.com@localhost (Christos Zoulas) wrote:

> On Sep 19,  8:13am, tls%panix.com@localhost (Thor Lancelot Simon) wrote:
> -- Subject: Re: high load, no bottleneck
> 
> | On Wed, Sep 18, 2013 at 06:03:11PM +0200, Emmanuel Dreyfus wrote:
> | > Emmanuel Dreyfus <manu%netbsd.org@localhost> wrote:
> | > 
> | > > Thank you for saving my day. But now what happens?
> | > > I note the SATA disks are in IDE emulation mode, and not AHCI.
> This is | > > something I need to try changing:
> | > 
> | > Switched to AHCI. Here is below how hard disks are discovered
> (the relevant raid | > is RAID1 on wd0 and wd1)
> | > 
> | > In this setup, vfs.wapbl.flush_disk_cache=1 still get high loads,
> on both 6.0 | > and -current. I assume there must be something bad
> with WAPBL/RAIDframe | 
> | There is at least one thing: RAIDframe doesn't allow enough
> simultaneously | pending transactions, so everything *really* backs
> up behind the cache flush. | 
> | Fixing that would require allowing RAIDframe to eat more RAM.  Last
> time I | proposed that, I got a rather negative response here.
> 
> sysctl to the rescue.

The appropriate 'bit to twiddle' is likely raidPtr->openings.
Increasing the value can be done while holding raidPtr->mutex.
Decreasing the value can also be done while holding raidPtr->mutex, but
will need some care if attempting to decrease it by more than the
number of outstanding IOs.

I'm happy to review any changes to this, but won't have time to code it
myself, unfortunately :( 

Later...

Greg Oster