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Date: Tue, 11 Nov 2008 20:49:41 -0800
From: Bruce Cran <bruce@cran.org.uk>
To: current@freebsd.org, jkoshy@freebsd.org
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Subject: hwpmc deadlock: processes hang on pmc-sx
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I decided to try hwpmc today, but ran into a
deadlock on the second run.  I'm using a dual core laptop:

CPU: AMD Turion(tm) 64 X2 Mobile Technology TL-52 (1600.07-MHz K8-class
CPU) Origin = "AuthenticAMD"  Id = 0x40f82  Stepping = 2
  Features=0x178bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2,HTT>
  Features2=0x2001<SSE3,CX16>
  AMD
Features=0xea500800<SYSCALL,NX,MMX+,FFXSR,RDTSCP,LM,3DNow!+,3DNow!> AMD
Features2=0x1f<LAHF,CMP,SVM,ExtAPIC,CR8> Cores per package: 2
usable memory = 2071433216 (1975 MB)
avail memory  = 2001584128 (1908 MB)
ACPI APIC Table: <PTLTD          APIC  >
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
 cpu0 (BSP): APIC ID:  0
 cpu1 (AP): APIC ID:  1

uname:
FreeBSD tau.draftnet 8.0-CURRENT FreeBSD 8.0-CURRENT #0: Sun Nov  9
13:12:06 PST 2008
brucec@tau.draftnet:/usr/obj/usr/src/sys/MYKERNEL_8  amd64

I ran the command 
pmcstat -O test.stat -n 32768 -S instructions

I found that I couldn't quit pmcstat and any attempt to run new
processes hung too.  The 'ps' listing in ddb
contained the following:

State     wmesg     cmd
Ss       pmc-sx     sh
S        piperd     cron
S        pmc-sx     cron
S        pmc-sx     gconf-d
T+       pmc-sx     dmesg
S+       pmc-sx     top
SL       pmcloop    [hwpmc]
S+       pmcctx     pmcstat

Are there any commands I should run at the debugger to
collect more information if I trigger it again?

-- 
Bruce Cran