Date: Mon, 03 Mar 2003 14:49:21 -0500 (EST) From: John Baldwin <jhb@FreeBSD.org> To: Juli Mallett <jmallett@FreeBSD.org> Cc: current@FreeBSD.org, Hiten Pandya <hiten@unixdaemons.com> Subject: Re: Possible patch for limiting APs at startup Message-ID: <XFMail.20030303144921.jhb@FreeBSD.org> In-Reply-To: <20030301200615.A63428@FreeBSD.org>
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On 02-Mar-2003 Juli Mallett wrote:
> * De: Hiten Pandya <hiten@unixdaemons.com> [ Data: 2003-03-01 ]
> [ Subjecte: Possible patch for limiting APs at startup ]
>> Hello.
>>
>> Just as the topic says, do you think this patch is good enough, or gets
>> even close to it? I have tested the patch, and it seems to do it's job
>> in the right way. Some might call it hackery, but it's better than
>> nothing I would suppose.
>
> I think your use of "cpus" to refer to APs only is silly, and also that
> overriding mp_naps instead of using a real cpus value and using it as
> a bounds check akin to MAXCPU, is a bit of the wrong direction. As you
> know, the following is my patch, and it does not work, but I think,
> personally, the behaviour is saner, in theory at least :)
You should set mp_maxcpus prior to the mp_naps test so it isn't left
invalid in the common case. Also, this patch doesn't limit HT cpu's
at all. I could have a 4 cpu system with HTT and maxcpus=2, and I
will end up with 4 CPU's due to 2 logical CPU's per processor. Perhaps
this is intentional?
> %%%
> Index: mp_machdep.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/i386/i386/mp_machdep.c,v
> retrieving revision 1.203
> diff -d -c -r1.203 mp_machdep.c
> *** mp_machdep.c 24 Feb 2003 14:36:03 -0000 1.203
> --- mp_machdep.c 2 Mar 2003 00:22:58 -0000
> ***************
> *** 249,254 ****
> --- 249,259 ----
> /** XXX FIXME: what system files declare these??? */
> extern struct region_descriptor r_gdt, r_idt;
>
> + int mp_maxcpus = 0; /* max CPUs; not in BSS so it can be hacked. */
> + TUNABLE_INT("machdep.smp_max_cpus", &mp_maxcpus);
> + SYSCTL_INT(_machdep, OID_AUTO, smp_max_cpus, CTLFLAG_RD,
> + &mp_maxcpus, 1, "Maximum number of CPUs to use.");
> +
> int bsp_apic_ready = 0; /* flags useability of BSP apic */
> int mp_naps; /* # of Applications processors */
> int mp_nbusses; /* # of busses */
> ***************
> *** 864,874 ****
> }
> }
>
> ! /* qualify the numbers */
> ! if (mp_naps > MAXCPU) {
> printf("Warning: only using %d of %d available CPUs!\n",
> ! MAXCPU, mp_naps);
> ! mp_naps = MAXCPU;
> }
>
> /* See if we need to fixup HT logical CPUs. */
> --- 869,881 ----
> }
> }
>
> ! /* use the smallest number of requested CPUs or CPUs we support. */
> ! if ((mp_maxcpus > 0 && mp_naps > mp_maxcpus) || mp_naps > MAXCPU) {
> ! if (mp_maxcpus <= 0)
> ! mp_maxcpus = MAXCPU;
> printf("Warning: only using %d of %d available CPUs!\n",
> ! mp_maxcpus, mp_naps);
> ! mp_naps = mp_maxcpus;
> }
>
> /* See if we need to fixup HT logical CPUs. */
> %%%
>
> Thanx,
> juli.
> --
> Juli Mallett <jmallett@FreeBSD.org> - AIM: BSDFlata -- IRC: juli on EFnet
> OpenDarwin, Mono, FreeBSD Developer - ircd-hybrid Developer, EFnet addict
> FreeBSD on MIPS-Anything on FreeBSD - /* XXX Nothing to see here, now. */
>
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--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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