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    SubjectRe: [PATCH -tip-rcu] Make rcutorture more vicious: make quiescent rcutorture less power-hungry
    On Sun, Jun 22, 2008 at 10:06 PM, Paul E. McKenney
    <paulmck@linux.vnet.ibm.com> wrote:
    > This patch makes the non-module rcutorture a bit more friendly to
    > the power-conservation code. This is a rather simple-minded approach.
    > More sophisticated approaches would get rid of the rcutorture tasks
    > while rcutorture execution was suppressed, but attempts thus far to
    > do this have not gone well -- calling rcu_torture_init() from a /proc
    > callout results in oopses.

    Hi Paul,

    I applied your three patches

    [PATCH] Make rcutorture more vicious: add stutter feature
    [PATCH] Make rcutorture more vicious: reinstate boot-time testing
    [PATCH -tip-rcu] Make rcutorture more vicious: make quiescent
    rcutorture less power-hungry

    to v2.6.26-rc7 and gave it a quick testing in qemu. But it seems to
    hang during gdb self-tests at boot:

    rcu-torture:--- Start of test: nreaders=6 nfakewriters=4
    stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval=3
    stutter=5
    Clocksource tsc unstable (delta = 617797275 ns)
    Total HugeTLB memory allocated, 0
    Installing knfsd (copyright (C) 1996 okir@monad.swb.de).
    NTFS driver 2.1.29 [Flags: R/O].
    msgmni has been set to 228
    io scheduler noop registered
    io scheduler anticipatory registered
    io scheduler deadline registered
    io scheduler cfq registered (default)
    pci 0000:00:00.0: Limiting direct PCI/PCI transfers
    pci 0000:00:01.0: PIIX3: Enabling Passive Release
    pci 0000:00:01.0: Activating ISA DMA hang workarounds
    pci 0000:00:02.0: Boot video device
    Real Time Clock Driver v1.12ac
    Linux agpgart interface v0.103
    Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing disabled
    serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16450
    FDC 0 is a S82078B
    brd: module loaded
    loop: module loaded
    kgdb: Registered I/O driver kgdbts.
    kgdbts:RUN plant and detach test

    <--- full stop


    gdb shows this:

    kgdb_handle_exception (evector=0, signo=<value optimized out>,
    ecode=<value optimized out>, regs=0xc0769eec)
    at include/asm/processor.h:688
    688 asm volatile("rep; nop" ::: "memory");
    (gdb) bt
    #0 kgdb_handle_exception (evector=0, signo=<value optimized out>,
    ecode=<value optimized out>, regs=0xc0769eec)
    at include/asm/processor.h:688
    #1 0xc011ffa1 in kgdb_notify (self=<value optimized out>, cmd=9,
    ptr=0xc0769e30) at arch/x86/kernel/kgdb.c:478
    #2 0xc014f527 in notifier_call_chain (nl=<value optimized out>, val=9,
    v=0xc0769e30, nr_to_call=-1, nr_calls=0x0) at kernel/notifier.c:85
    #3 0xc014f925 in __atomic_notifier_call_chain (nh=<value optimized out>,
    val=9, v=0xc0769e30, nr_to_call=-1, nr_calls=0x0) at kernel/notifier.c:174
    #4 0xc014f95a in atomic_notifier_call_chain (nh=0x2, val=0, v=0xffffffff)
    at kernel/notifier.c:183
    #5 0xc014f98d in notify_die (val=0, str=<value optimized out>,
    regs=<value optimized out>, err=0, trap=0, sig=8) at kernel/notifier.c:564
    #6 0xc010a8e8 in do_divide_error (regs=0xc0769eec, error_code=0)
    at arch/x86/kernel/traps_32.c:594
    #7 0xc058cdba in page_fault ()
    #8 0xc080f780 in per_cpu__init_tss ()
    #9 0xc013c255 in do_softirq () at kernel/softirq.c:271
    #10 0xc013c255 in do_softirq () at kernel/softirq.c:271
    #11 0xc013c3f5 in irq_exit () at kernel/softirq.c:310
    #12 0xc011db28 in smp_apic_timer_interrupt (regs=<value optimized out>)
    at arch/x86/kernel/apic_32.c:619
    #13 0xc0108ed3 in apic_timer_interrupt () at include/asm/desc.h:309
    #14 0xc0106ce0 in ?? () at arch/x86/kernel/process_32.c:466
    #15 0xc0768000 in ?? ()
    #16 0x00000000 in ?? ()

    Without your patches, the kernel gets through here just fine.

    These are my RCU-related options:

    $ grep RCU .config
    # CONFIG_CLASSIC_RCU is not set
    CONFIG_PREEMPT_RCU=y
    CONFIG_RCU_TRACE=y
    CONFIG_RCU_TORTURE_TEST=y
    CONFIG_RCU_TORTURE_TEST_RUNNABLE=y

    As a convenience feature, it would be nice to have a boot option
    controlling the run-at-boot as well, simply because it saves a
    recompile for me :-) Actually, for some reason, the test still starts
    at boot even when CONFIG_RCU_TORTURE_TEST_RUNNABLE=n. Is a hunk
    missing from patch #2?


    Vegard

    --
    "The animistic metaphor of the bug that maliciously sneaked in while
    the programmer was not looking is intellectually dishonest as it
    disguises that the error is the programmer's own creation."
    -- E. W. Dijkstra, EWD1036


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