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Date: Fri, 10 Dec 2010 17:03:27 +0200
From: Andriy Gapon <avg@freebsd.org>
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Cc: freebsd-hackers@freebsd.org, freebsd-geom@freebsd.org
Subject: Re: Where userland read/write requests, whcih is larger than MAXPHYS,
 are splitted?
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on 10/12/2010 16:48 Andriy Gapon said the following:
> But maybe I misunderstood your question and you talked about a different I/O layer
> or different I/O path.
> 

Oh, probably you talk about physread/physwrite == physio.
Indeed, it issues bio-s with max size of si_iosize_max and runs them sequentially.
 Besides, if uio is really "vectored", then each uio sub-buffer is processed
sequentially too.
This is probably less fast than running the requests in parallel; plus side could
be that less KVA is required for mapping user space buffer (UIO_USERSPACE case)
into kernel.  Not sure if the latter is much of concern though.  The sequential
code is simpler too :-)

-- 
Andriy Gapon