Date: Sun, 14 Dec 2014 12:22:09 -0800 From: Alfred Perlstein <bright@mu.org> To: Ian Lepore <ian@FreeBSD.org> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: i386 PAE kernel works fine on 10-stable Message-ID: <705D7AEE-D0D6-477B-80F5-746E2B1104B2@mu.org> In-Reply-To: <1418587165.977.0.camel@freebsd.org> References: <1418579278.2026.9.camel@freebsd.org> <DB7FB000-9A82-41F5-A4BD-6806AF218F01@mu.org> <1418580756.2026.12.camel@freebsd.org> <847BD158-0867-4F5F-83A9-1651E77D29EF@mu.org> <1418587165.977.0.camel@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Dec 14, 2014, at 11:59 AM, Ian Lepore wrote: > On Sun, 2014-12-14 at 10:53 -0800, Alfred Perlstein wrote: >> On Dec 14, 2014, at 10:12 AM, Ian Lepore wrote: >>=20 >>> On Sun, 2014-12-14 at 10:09 -0800, Alfred Perlstein wrote: >>>> On Dec 14, 2014, at 9:47 AM, Ian Lepore wrote: >>>>=20 >>>>> This is an out of the blue FYI post to let people know that = despite all >>>>> the misinformation you'll run across if you search for information = on >>>>> FreeBSD PAE support, it (still) works just fine. I've been using = it >>>>> (for reasons related to our build system and products at $work) = since >>>>> 2006, and I can say unequivocally that it works fine on 6.x, 8.x, = and >>>>> now 10.x (and presumably on the odd-numbered releases too but I've = never >>>>> tried those). >>>>>=20 >>>>> In my most recent testing with 10-stable, I found it was = compatible with >>>>> drm2 and radeonkms drivers and I was able to run Xorg and gnome = just >>>>> fine. All my devices, and apps, and even the linuxulator worked = just >>>>> fine. >>>>>=20 >>>>> One thing that changed somewhere between 8.4 and 10.1 is that I = had to >>>>> add a kernel tuning option to my kernel config: >>>>>=20 >>>>> option KVA_PAGES=3D768 # Default is 512 >>>>>=20 >>>>> I suspect that the most frequent use of PAE is on laptops that = have 4gb >>>>> and the default tuning is adequate for that. My desktop machine = has >>>>> 12gb and I needed to bump up that value to avoid errors related to = being >>>>> unable to create new kernel stacks. >>>>>=20 >>>>=20 >>>> There already is a #define that is bifurcated based on PAE in = pmap.h: >>>>=20 >>>> #ifndef KVA_PAGES >>>> #ifdef PAE >>>> #define KVA_PAGES 512 >>>> #else >>>> #define KVA_PAGES 256 >>>> #endif >>>> #endif >>>>=20 >>>> Do you think it will harm things to apply your suggested default to = this file? >>>>=20 >>>=20 >>> I would have to defer to someone who actually understands just what = that >>> parm is tuning. It was purely speculation on my part that the = current >>> default is adequate for less memory than I have, and I don't know = what >>> that downside might be for setting it too high. >>>=20 >>=20 >> KVA pages is the amount of pages reserved for kernel address space: >>=20 >> * Size of Kernel address space. This is the number of page table = pages >> * (4MB each) to use for the kernel. 256 pages =3D=3D 1 Gigabyte. >> * This **MUST** be a multiple of 4 (eg: 252, 256, 260, etc). >> * For PAE, the page table page unit size is 2MB. This means that 512 = pages >> * is 1 Gigabyte. Double everything. It must be a multiple of 8 for = PAE. >>=20 >> It appears that our default for PAE leaves 1GB for kernel address to = play with? That's an interesting default. Wonder if it really makes = sense for PAE since the assumption is that you'll have >4GB ram in the = box, wiring down 1.5GB for kernel would seem to make sense=85 Probably = make sense to ask Peter or Alan on this. >>=20 >> Also wondering how bad it would be to make these tunables, I see they = trickle down quite a bit into the system, hopefully not defining some = static arrays, but I haven't dived down that far. >>=20 >> Ian, just to understand better, how much memory is in your machine? >>=20 >=20 > 12GB. Another option to keep things simple it might make sense to add a kernel = conf for PAE-12GLARGER and just include the PAE kernel and set your = tunable. =20 That will keep people with "small PAE" (6G) from perhaps experiencing = changes while still allowing larger PAE customers to tune properly. Adding a note to the top of the PAE kernel stating "this works well for = machines with less than 12GB, but for larger systems you want = PAE-12GLARGER". -Alfred=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?705D7AEE-D0D6-477B-80F5-746E2B1104B2>