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Date:      Tue, 25 Dec 2012 22:48:54 +0200
From:      Konstantin Belousov <kostikbel@gmail.com>
To:        Robert Watson <rwatson@freebsd.org>
Cc:        alc@freebsd.org, arch@freebsd.org, Alan Cox <alc@rice.edu>
Subject:   Re: Unmapped I/O
Message-ID:  <20121225204854.GE82219@kib.kiev.ua>
In-Reply-To: <alpine.BSF.2.00.1212252040270.56707@fledge.watson.org>
References:  <20121219135451.GU71906@kib.kiev.ua> <CAJUyCcNuD_TWR6xxFxVqDi4-eBGx3Jjs21eBxaZYYVUERESbMw@mail.gmail.com> <alpine.BSF.2.00.1212190923170.2005@desktop> <50D22EA6.1040501@rice.edu> <alpine.BSF.2.00.1212252040270.56707@fledge.watson.org>

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On Tue, Dec 25, 2012 at 08:42:27PM +0000, Robert Watson wrote:
> On Wed, 19 Dec 2012, Alan Cox wrote:
>=20
> >> Are the machines that don't have a direct map performance critical? My=
=20
> >> expectation is that they are legacy or embedded.  This seems like a gr=
eat=20
> >> project to do when the rest of the pieces are stable and fast. Until t=
hen=20
> >> they could just use something like pbufs?
> >
> > I think the answer to your first question depends entirely on who you a=
re.=20
> > :-)  Also, at the low-end of the server space, there are many people tr=
ying=20
> > to promote arm-based systems.  While FreeBSD may never run on your arm-=
based=20
> > phone, I think that ceding the arm-based server market to others will b=
e a=20
> > strategic mistake.
> >
> > Alan
> >
> > P.S. I think we're moving the discussion to far away from kib's origina=
l, so=20
> > I suggest changing the subject line on any follow ups.
>=20
> Despite moving the discussion a little further away: MIPS-based
> systems, a direct mapped map segment (e.g., kseg, xkphys, etc) is part
> of the underlying design and doesn't rely on any TLB entries at all.
> We run much of the kernel from direct map regions to avoid causing TLB
> pressure.
Yes, as it was noted already, 32bit mips kseg is not much usable on
the mips systems with more than 1GB of RAM. But Alan' another patch,
with, I believe, small modification, could provide the gain there too.

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