From owner-freebsd-current@FreeBSD.ORG  Tue Mar 23 08:56:27 2010
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To: Pawel Jakub Dawidek <pjd@FreeBSD.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Tue, 23 Mar 2010 00:36:07 +0100."
	<20100322233607.GB1767@garage.freebsd.pl> 
Date: Tue, 23 Mar 2010 08:56:24 +0000
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Cc: Alexander Motin <mav@FreeBSD.org>, freebsd-current@FreeBSD.org,
	Andriy Gapon <avg@icyb.net.ua>, freebsd-arch@FreeBSD.org
Subject: Re: Increasing MAXPHYS 
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In message <20100322233607.GB1767@garage.freebsd.pl>, Pawel Jakub Dawidek write
s:

>A class is suppose to interact with other classes only via GEOM, so I
>think it should be safe to choose g_up/g_down threads for each class
>individually, for example:
>
>	/dev/ad0s1a (DEV)
>	       |
>	g_up_0 + g_down_0
>	       |
>	     ad0s1a (BSD)
>	       |
>	g_up_1 + g_down_1
>	       |
>	     ad0s1 (MBR)
>	       |
>	g_up_2 + g_down_2
>	       |
>	     ad0 (DISK)

Uhm, that way you get _more_ context switches than today, today g_down
will typically push the requests all the way down through the stack
without a context switch.  (Similar for g_up)


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.