Re: CVS commit: [tls-maxphys] src/sys/ufs/ufs

[Thor Lancelot Simon <tls%netbsd.org@localhost>]

On Mon, Oct 15, 2012 at 04:24:54PM +0200, Manuel Bouyer wrote:
> 
> I wonder if we could reuse bits from the read-ahead code for write-behind ?

I'm not sure the read-ahead code is working properly.  When I read through
the filesystem with cat or dd bs=1024k, on a device (wd on ahcisata)
that can do 1M transfers, I see that most transfers are considerably
smaller.

What I'm more worried about is that it may _never_ be a good idea, in the
general case, to put 1M transfers on the bus, particularly single writes,
since they may delay things like log transactions in the disk's write
cache.  We might need a much safer I/O scheduler before we can safely do
this.  Or we might need to let the user tune it on a per-filesystem basis.

Thor