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    SubjectRe: Performance/resume issues on Toshiba NB305
    Would be helpful to Cc the people that may help you.


    On Fri, Feb 25, 2011 at 10:42:39AM -0600, Seth Forshee wrote:
    > I've been looking into a couple of problems with this machine that have
    > me a bit stumped at the moment. The two problems may or may not be
    > related, so I'm including details about both issues below. If anyone has
    > any ideas, I'd love to hear them. Note that these are not recent
    > regressions; they've been around since at least 2.6.32.
    >
    > The CPU in this machine is an Atom N450.
    >
    > When booted normally the performance on this machine is very poor, but
    > when booted with any of nohz=off, nolapic, or nohpet it improves
    > significantly. The performance also improves if I use the patch below to
    > force the hpet to remain in periodic mode (with hpet=periodic on the
    > command line).
    >
    > One other thing I noticed when I had added some logging related to hpet
    > rearming is 3-5 second periods of no log activity occurring fairly
    > frequently, whereas such inactive periods are infrequent when
    > performance is good and are also infrequent on another machine with very
    > similar hardware and no performance issues.
    >
    > The machine also hangs for 5 minutes during resume, unless booted with
    > both nohz=off and highres=off, or with hpet=periodic using the patch
    > below. I've traced this down to hanging in an SMI handler during the
    > ACPI _WAK method execution. The 5 minutes corresponds to how long it
    > takes for the low 32 bits of the hpet to wrap in this machine, and since
    > the options that eliminate the hang result in the hpet being in periodic
    > mode during _WAK method execution I suspect that the SMI handler is
    > hanging until a timer interrupt happens.
    >
    > One possible explanation here is that the performance problems are also
    > related to hangs in SMI handlers until there's a timer interrupt,
    > although I don't know how that explains why some of the command line
    > options eliminate the performance issues.

    Sounds like a buggy BIOS to me. Is there upgrades available for this
    box?

    -- Steve

    >
    > Note also that I've already looked into the triggering for IRQ0, and it
    > seems to be correct.
    >
    > Thanks,
    > Seth
    >
    >
    > diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
    > index 4ff5968..ab10012 100644
    > --- a/arch/x86/kernel/hpet.c
    > +++ b/arch/x86/kernel/hpet.c
    > @@ -87,6 +87,7 @@ static inline void hpet_clear_mapping(void)
    > static int boot_hpet_disable;
    > int hpet_force_user;
    > static int hpet_verbose;
    > +static int hpet_oneshot_disable;
    >
    > static int __init hpet_setup(char *str)
    > {
    > @@ -97,6 +98,8 @@ static int __init hpet_setup(char *str)
    > hpet_force_user = 1;
    > if (!strncmp("verbose", str, 7))
    > hpet_verbose = 1;
    > + if (!strncmp("periodic", str, 8))
    > + hpet_oneshot_disable = 1;
    > }
    > return 1;
    > }
    > @@ -306,6 +309,10 @@ static void hpet_legacy_clockevent_register(void)
    > hpet_clockevent.min_delta_ns = clockevent_delta2ns(HPET_MIN_PROG_DELTA,
    > &hpet_clockevent);
    >
    > + /* Disable one-shot mode if requested */
    > + if (hpet_oneshot_disable)
    > + hpet_clockevent.features &= ~CLOCK_EVT_FEAT_ONESHOT;
    > +
    > /*
    > * Start hpet with the boot cpu mask and make it
    > * global after the IO_APIC has been initialized.
    > diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    > index 48b2761..8e84c11 100644
    > --- a/kernel/time/tick-broadcast.c
    > +++ b/kernel/time/tick-broadcast.c
    > @@ -565,10 +565,15 @@ void tick_broadcast_switch_to_oneshot(void)
    >
    > raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
    >
    > - tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT;
    > bc = tick_broadcast_device.evtdev;
    > + if (bc && !(bc->features & CLOCK_EVT_FEAT_ONESHOT))
    > + goto unlock;
    > +
    > + tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT;
    > if (bc)
    > tick_broadcast_setup_oneshot(bc);
    > +
    > +unlock:
    > raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
    > }
    >


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