Date: Sun, 07 Oct 2001 09:28:16 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: Kazutaka YOKOTA <yokota@zodiac.mech.utsunomiya-u.ac.jp> Cc: Alfred Perlstein <bright@mu.org>, smp@freebsd.org Subject: Re: How to distinguish the SMP kernel and the UP kernel Message-ID: <XFMail.011007092816.jhb@FreeBSD.org> In-Reply-To: <200110060625.PAA02451@zodiac.mech.utsunomiya-u.ac.jp>
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On 06-Oct-01 Kazutaka YOKOTA wrote: > >>> - The following patch will add a new sysctl variable. >>> >>> kern.smp.kernel >>> >>> This will be 0 for the UP kernel and 1 for the SMP kernel. >>> >>> - It also make kern.smp.active available in the UP kernel as well. >>> (Previously this sysctl variable was only present in the SMP >>> kernel.) It will always be 0 for the UP kernel. >> >>This shouldn't be done. There's no need for 2 copies of the same sysctl. >>Actually, userland can _already_ tell if it is an SMP kernel or not by >>looking >>if the kern.smp.active sysctl exists. This is how top works, for example. >>Thus, userland doesn't need any of this. Only in the kernel do you need >>this. >> >>Now, ideally kernel modules shouldn't care if they are on a SMP kernel or >>not. > > I agree. But, some modules need to know ;-< I was trying to make > the pnpbios driver into a module and it has #ifdef SMP in it. Ah, ok. Yes, that might be a bit tricky in that case. :-) >>Why does the module in question care? The only thing I would do here is >>possibly export a global variable saying if SMP was compiled in, nothing >>more. > > This is fine, as I am not very much interested in exposing to the userland > which kernel configration, SMP or UP, is running. Fair enough. I really would prefer that the variable not be in subr_smp.c so that we don't have compile all of that file just for one variable in a UP kernel. I'm not sure of a better place, however. To avoid adding too many variables, I would suggest exporting smp_active in the UP case (but not the sysctl, as that might break things like top). > Kazu -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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