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Date: Sun, 10 Dec 2006 10:34:16 -0500 From: John Richard Moser <nigelenki@...cast.net> To: Arjan van de Ven <arjan@...radead.org> CC: linux-kernel@...r.kernel.org Subject: Re: PAE/NX without performance drain? -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Arjan van de Ven wrote: > On Sat, 2006-12-09 at 15:39 -0500, John Richard Moser wrote: >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA1 >> >> Apparently (as I've been told today) using a hardware NX bit in a 32-bit >> x86 kernel requires PAE mode. PAE mode is enabled with HIGHMEM64, which >> is (apparently) extremely slow. > > > it's not extremely slow. > > there is a minor performance delta, sure, but to be honest that's a > benchmark thing more than a real life thing. > > What did your measurements show that the slowdown was? And how did you > measure this? I didn't measure, I was told by various people on IRC. Also Google has some misleading facts: - Someone mentioned that HIGHMEM64G + 4G split costs 10%-30%. I immediately took that as "4G split might be friggin' expensive." - In some discussions Ingo mentioned HIGHMEM64G re RT preemption being a huge performance delta; but I haven't found evidence that this isn't a bug in RT. Too bad PAE can't be detected at boot time; someone else mentioned that some recent Pentium M laptops (and anything older than PPro) don't boot if PAE is on. Making 2 copies of the functions would be a pain in the ass; and using indirect addressing and function pointers would be... slow. In performance critical areas. I want my hardware NX bit working in Ubuntu without having to recompile my kernel dammit. How do I swing this one past them? The performance I can argue; breaking 586 and some random laptops (I've been contacted by someone who has several of these Pentium-M machines that die on PAE) I can't do. > > > > - -- We will enslave their women, eat their children and rape their cattle! -- Bosc, Evil alien overlord from the fifth dimension -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iQIVAwUBRXwo9ws1xW0HCTEFAQK7DA/+KOZavRjhhp0N8k+cj2E0YTT5f1HbV0wE mi0QqOwhR6VFg/8M+HGU5ytnmdXnNm5TyyTvxHfgEFaWpwMxWhAT0KZgP5twGc/9 f2uY9s600nvmDXnh9zKFsFBmIgJqdg++01cY9C6O2cl7xfTTvrzVXllZOBMtvKxh KmkHr0VVNhs2V4EYlEhKhMh2OAhYFtnUdd2VyV4d3snn4Y/Y/IneMM0GxULjGwg5 V7ATdJgs+s02iT8cRGFKbbn3H+0DtIxolIhlkvukPy0xfECtx/92HguLkLfq4o6I rRyP1n42vkY2wmKFtgnYU9CXBmd+1/GOmiVXk77+lID9xDQpWa5e3j4uB8o/StYv 6NMfj66Sc5yq/4+9lBB7awPA5gZkgBmYcTl4bvM5+FVxkr1pREUXzD589y9AEAoa fCVv0DXTZwDjYZBY9uFRZyRe0UVgPFwyBqq6S5QISXge242spGo6G9QJKj25vsMY JYdJb6f0EFzqwcFhYy+pp5s2NAId1lPT6SxhPq9aJ36enI8j4vJHPHSM8yBdVGSP g8OzFLb9EYTKvSzdTN1JwAMkGvwGKcfY+tEIEUlTEb0wqwEfA3rClWdb4ikEBl5D G2kjPqlGCdOXjIkijSzu8d6w7jPa+/EhdWRnBxuP/H7iKLWJoxaMqOR27nVx7/Fo OiJeilQNMMA= =+GiD -----END PGP SIGNATURE----- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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