Re: write alignment matters?

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Thu, Jun 23, 2011 at 03:36:25PM +0700, Robert Elz wrote:
>     Date:        Wed, 22 Jun 2011 19:30:55 -0400 (EDT)
>     From:        der Mouse <mouse%Rodents-Montreal.ORG@localhost>
>     Message-ID:  
> <201106222330.TAA28359%Sparkle.Rodents-Montreal.ORG@localhost>
> 
>   | But the interface is much older than that, and, even if it's not
>   | codified, there's a lot of history behind the notion that userland
>   | alignment of write() buffers affects, at most, performance, to the
>   | point where I consider it part of the interface.
> 
> Not on access to raw devices it isn't, and never was - what Erik Fair
> said (Message-id: <5F005E6A-5441-4BEC-BB3C-4A9B79584BFB%netbsd.org@localhost>)
> was 100% correct - if you're using a raw device, it is up to the
> application to meet whatever the requirements of that particular device
> are, because one of the properties of raw devices is that they don't
> do any kind of rebuffering of data (and the driver must not - that is
> a part of the interface contract).

That doesn't seem like it can really be right.  There are plenty of
systems where devices cannot DMA from user addresses.

Thor