Date: Tue, 25 Dec 2012 18:19:15 -0700 From: Warner Losh <imp@bsdimp.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: alc@freebsd.org, arch@freebsd.org, Robert Watson <rwatson@freebsd.org>, Alan Cox <alc@rice.edu> Subject: Re: Unmapped I/O Message-ID: <58BA8294-A610-4474-A8B4-9AF69AD44779@bsdimp.com> In-Reply-To: <20121225204854.GE82219@kib.kiev.ua> 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> <20121225204854.GE82219@kib.kiev.ua>
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On Dec 25, 2012, at 1:48 PM, Konstantin Belousov wrote: > On Tue, Dec 25, 2012 at 08:42:27PM +0000, Robert Watson wrote: >> On Wed, 19 Dec 2012, Alan Cox wrote: >> >>>> Are the machines that don't have a direct map performance critical? My >>>> expectation is that they are legacy or embedded. This seems like a great >>>> project to do when the rest of the pieces are stable and fast. Until then >>>> they could just use something like pbufs? >>> >>> I think the answer to your first question depends entirely on who you are. >>> :-) Also, at the low-end of the server space, there are many people trying >>> to promote arm-based systems. While FreeBSD may never run on your arm-based >>> phone, I think that ceding the arm-based server market to others will be a >>> strategic mistake. >>> >>> Alan >>> >>> P.S. I think we're moving the discussion to far away from kib's original, so >>> I suggest changing the subject line on any follow ups. >> >> 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. Most mips move to 64-bit when they have more than 512MB or 1GB because the direct map is just too handy... Warnerhelp
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