Re: raw/block device disc troughput

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Thu, 24 May 2012, Thor Lancelot Simon wrote:

> On Thu, May 24, 2012 at 05:31:43PM +0000, Eduardo Horvath wrote:
> > 
> > With large transfers (larger than MAXPHYS) the writes are split up into 
> > MAXPHYS chunks and the disk handles them in parallel, hence the 
> > performance increase even beyond MAXPHYS.
> 
> Is this actually true?  For requests from userspace via the raw device,
> does physio actually issue the smaller chunks in parallel?

Depends... this case it's true.  physio() breaks the iov into chunks and 
allocates a buf for each chunk and calls the strategy() routine on each 
buf without waiting for completion.  So on a controller that does tagged 
queuing they run in parallel.

Eduardo