From owner-freebsd-hackers  Mon Jun  7 23:36:15 1999
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To: Zhihui Zhang <zzhang@cs.binghamton.edu>
Subject: Re: The choice of MAXPHYS 
Cc: freebsd-hackers@FreeBSD.ORG
In-reply-to: Your message of "Thu, 03 Jun 1999 10:40:10 EDT."
		<Pine.GSO.3.96.990603101914.28480A-100000@sol.cs.binghamton.edu> 
References: <Pine.GSO.3.96.990603101914.28480A-100000@sol.cs.binghamton.edu>  
Date: Tue, 08 Jun 1999 00:34:01 -0600
From: Warner Losh <imp@harmony.village.org>
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In message
<Pine.GSO.3.96.990603101914.28480A-100000@sol.cs.binghamton.edu>
Zhihui Zhang writes: 
: The value of MAXPHYS is chosen to be 64K for the maximum raw I/O transfer
: size. I am wondering why it is not set larger.

I don't think that it is possible to guarantee that you can do a
larger write than 64k on a aha-1542 card given the worst case scatter
gather list you can have in FreeBSD.  I think that this used to be a
common limit.  I thought CAM raised the limit somewhat on cards that
could support it.

Warner


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