Date: Sun, 13 Jan 2008 22:08:25 -0500 From: Joe Marcus Clarke <marcus@FreeBSD.org> To: Peter Jeremy <peterjeremy@optushome.com.au> Cc: Kostik Belousov <kostikbel@gmail.com>, current <current@FreeBSD.org>, Igor Mozolevsky <igor@hybrid-lab.co.uk> Subject: Re: RFC: Adding a hw.features[2] sysctl Message-ID: <1200280105.7836.16.camel@shumai.marcuscom.com> In-Reply-To: <20080113182457.GN929@server.vk2pj.dyndns.org> References: <1200197787.67286.13.camel@shumai.marcuscom.com> <20080113064450.GW57756@deviant.kiev.zoral.com.ua> <20080113182457.GN929@server.vk2pj.dyndns.org>
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--=-ZiOdBNAAe01gkc+60Kxp Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Mon, 2008-01-14 at 05:24 +1100, Peter Jeremy wrote: > On Sun, Jan 13, 2008 at 08:44:50AM +0200, Kostik Belousov wrote: > >On Sat, Jan 12, 2008 at 11:16:27PM -0500, Joe Marcus Clarke wrote: > >> I find it would be useful to have the list of CPU features available v= ia > >> a sysctl. Currently, he only ways to get this information are to have > >> linprocfs mounted, or parse dmesg.boot (if it exists). Attached are > >Not quite true, since the raw CPU capabilities are accessible using > >the cpuid instruction, both to the kernel- and user-mode. >=20 > >> patches to add hw.features and hw.features2 sysctls for i386 and amd64 > >> (where a list of CPU features is applicable). The results are identic= al > >> to the Features and Features2 strings from dmesg: > >>=20 > >> hw.features2: 0x41d<SSE3,RSVD2,MON,DS_CPL,CNXT-ID> > >> hw.features: > >> 0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CM= OV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE> > > > >The only part that I do not fully agree is to dedicate 1Kb of the kernel > >memory to the strings that could be reconstructed in the usermode and > >are relatively rare used. >=20 > All the required strings are already part of identcpu.c so the only > overhead would be either a ~200 byte chunk of KVA to store a copy of > the identcpu output as a SYSCTL_STRING or a SYSCTL_PROC wrapper > around the relevant parts of identcpu.c Agreed, the memory footprint could be made much smaller than in my patch. I think a string would be fine. I think a proc might be overkill as this information will not change. >=20 > >I would suggest either export only bitmask of the cpu features and do > >the formatting in the sysctl(8), >=20 > A userland program could perform the cpuid functions itself just as > easily as extracting the information from a sysctl. It would be easy to export just the bitmask, and leave the parsing up to the consumer. However, I think the strings would be more script friendly. >=20 > >The first option could be preferable, since kernel might disable some > >features, that is not reflected in the output of cpuid instruction. > >Example of this would be identcpu.c, line 860 (HTT on AMD). >=20 > This depends whether you want to know what features are available on > the CPU or what features are available in the currently running kernel. > In Peter's case, there was a requirement to know the CPU capabilities. > OTOH, something like mplayer wants to know what features it can use > whilst it's currently executing. I had thought of making the output identical what is seen in dmesg's Features[2] lines. This shows the features that are available on the CPU. Thanks to everyone who has replied so far. The comments have been helpful. Joe >=20 > On Sun, Jan 13, 2008 at 12:21:02PM +0000, Igor Mozolevsky wrote: > >Would /dev/cpuinfo not be more appropriate for this? >=20 > IMHO, no. Virtually all similar FreeBSD information is exported via > sysctl and this sort of information fits neatly into the existing > MIB tree as either dev.cpu.N.features or hw.cpu.features >=20 --=20 Joe Marcus Clarke FreeBSD GNOME Team :: gnome@FreeBSD.org FreeNode / #freebsd-gnome http://www.FreeBSD.org/gnome --=-ZiOdBNAAe01gkc+60Kxp Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (FreeBSD) iD8DBQBHitIpb2iPiv4Uz4cRAvkuAJ9m7x2rOHq6Hz7yyA7IJachBNmfzgCffV4B wSV2xTy8ZLlmr8936ZCRat0= =mlXp -----END PGP SIGNATURE----- --=-ZiOdBNAAe01gkc+60Kxp--
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