linux-kernel - Re: [PATCH -tip-rcu] Make rcutorture more vicious: make quiescent rcutorture less power-hungry

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Date:	Sun, 22 Jun 2008 22:58:05 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, josh@...edesktop.org,
	dvhltc@...ibm.com, niv@...ibm.com, dino@...ibm.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	adobriyan@...il.com, oleg@...sign.ru, bunk@...nel.org, rjw@...k.pl
Subject: Re: [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@...ux.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@...ad.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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