Date: Thu, 21 Apr 2011 03:02:09 +1000 (EST) From: Ian Smith <smithi@nimnet.asn.au> To: Daniel Gerzo <danger@freebsd.org> Cc: Alexander Motin <mav@freebsd.org>, freebsd-stable@freebsd.org Subject: kern.smp.maxid error on i386 UP [was: powerd / cpufreq question] Message-ID: <20110420164100.Y43371@sola.nimnet.asn.au> In-Reply-To: <20110413024230.Y35056@sola.nimnet.asn.au> References: <4D9EEDAF.3020803@rulez.sk> <20110411125416.S35056@sola.nimnet.asn.au> <4DA37E31.4020700@FreeBSD.org> <20110413024230.Y35056@sola.nimnet.asn.au>
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On Wed, 13 Apr 2011, Ian Smith wrote: > On Tue, 12 Apr 2011, Daniel Gerzo wrote: > > On 11.4.2011 6:08, Ian Smith wrote: [..] > > > Are those kern.cp_times values as they came, or did you remove trailing > > > zeroes? Reason I ask is that on my Thinkpad T23, single-core 1133/733 > > > MHz, sysctl kern.cp_time shows the usual 5 values, but kern.cp_times has > > > the same 5 values for cpu0, but then 5 zeroes for each of cpu1 through > > > cpu31, on 8.2-PRE about early January. I need to update the script to > > > remove surplus data for non-existing cpus, but wonder if the extra data > > > also appeared on your 12 core box? > > > > I haven't removed anything, it's a pure copy&paste. > > Thanks. I'll check the single-cpu case again after updating to 8.2-R Ok, still a problem on at least my i386 single core Thinkpad T23 at 8.2-R, since 8.0 I think, certainly evident in a sysctl -a at 8.1-R FreeBSD t23.smithi.id.au 8.2-RELEASE FreeBSD 8.2-RELEASE #1: Thu Apr 14 21:45:47 EST 2011 root@t23.smithi.id.au:/usr/obj/usr/src/sys/GENERIC i386 Verbose dmesg: http://smithi.id.au/t23_dmesg_boot-v.8.2-R.txt sysctl -a: http://smithi.id.au/t23_sysctl-a_8.2-R.txt kern.ccpu: 0 <cpu count="1" mask="0x1">0</cpu> kern.smp.forward_signal_enabled: 1 kern.smp.topology: 0 kern.smp.cpus: 1 kern.smp.disabled: 0 kern.smp.active: 0 kern.smp.maxcpus: 32 kern.smp.maxid: 31 <<<<<<< hw.ncpu: 1 kern.cp_times: 38548 1 120437 195677 9660939 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 /usr/src/sys/kern/kern_clock.c: return SYSCTL_OUT(req, 0, sizeof(long) * CPUSTATES * (mp_maxid + 1)); Consumers of kern.cp_times like powerd, top, dtrace? and others have to loop over 32 cpus, all but one non-existent, and there seem to be many places in the kernel doing eg: for (cpu = 0; cpu <= mp_maxid; cpu++) { and while CPU_FOREACH / CPU_ABSENT will skip over them, seems wasteful at best on machines least likely to have cycles to spare. eg: powerd parses kern.cp_times to count cpus, wasting cycles adding up the 31 'empty' cpus. I haven't explored other userland consumers. Clearly kern.smp.maxid (ie mp_maxid) should be 0, not 31. On i386, non-APIC i386 at least, mp_maxid is not set to (mp_ncpus - 1) as on some other archs .. after having being initialised to (MAXCPU - 1) in /sys/i386/i386/mp_machdep.c it's never updated for non-smp machines. I haven't chased all of these rabbits down all of their holes by any means, but it seems that making /sys/i386/i386/mp_machdep.c do what it says it's gonna do ('with an id of 0') should help. Paste, tabs lost: int cpu_mp_probe(void) { /* * Always record BSP in CPU map so that the mbuf init code works * correctly. */ all_cpus = 1; if (mp_ncpus == 0) { /* * No CPUs were found, so this must be a UP system. Setup * the variables to represent a system with a single CPU * with an id of 0. */ mp_ncpus = 1; + mp_maxid = 0; return (0); } /* At least one CPU was found. */ if (mp_ncpus == 1) { /* * One CPU was found, so this must be a UP system with * an I/O APIC. */ + mp_maxid = 0; return (0); } /* At least two CPUs were found. */ return (1); } Note that the second added line above already exists in /sys/amd64/amd64/mp_machdep.c, maybe to fix a similar problem, though that should only apply to 'a UP system with an I/O APIC'. Maybe better could be to fix this in cpu_mp_probe's caller, /sys/kern/subr_smp.c: static void mp_start(void *dummy) { mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN); /* Probe for MP hardware. */ if (smp_disabled != 0 || cpu_mp_probe() == 0) { mp_ncpus = 1; + mp_maxid = 0; all_cpus = PCPU_GET(cpumask); return; } cpu_mp_start(); printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n", mp_ncpus); cpu_mp_announce(); } I'm probably a long way off base for a solution, but think I've located the problem. Thoughts? Is this a known issue? Might any developers actually still have a single-cpu i386 system to check this on? :) Very happy to test any patches etc. cheers, Ian
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