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Message-ID: <874j842bqq.ffs@tglx>
Date: Thu, 01 Aug 2024 23:07:25 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: David Woodhouse <dwmw2@...radead.org>, mikelley@...rosoft.com, kvm
<kvm@...r.kernel.org>
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, decui@...rosoft.com,
haiyangz@...rosoft.com, kys@...rosoft.com, linux-hyperv@...r.kernel.org,
linux-kernel@...r.kernel.org, lirongqing@...du.com, mingo@...hat.com,
seanjc@...gle.com, wei.liu@...nel.org, x86@...nel.org
Subject: Re: [PATCH] clockevents/drivers/i8253: Do not zero timer counter in
shutdown
On Thu, Aug 01 2024 at 16:22, David Woodhouse wrote:
> On Thu, 2024-08-01 at 10:00 +0100, David Woodhouse wrote:
> bool __init pit_timer_init(void)
> {
> - if (!use_pit())
> + if (!use_pit()) {
> + if (!hypervisor_is_type(X86_HYPER_NATIVE)) {
> + /*
> + * Don't just ignore the PIT. Ensure it's stopped,
> + * because VMMs otherwise steal CPU time just to
> + * pointlessly waggle the (masked) IRQ.
> + */
> + raw_spin_lock(&i8253_lock);
> + outb_p(0x30, PIT_MODE);
> +
> + /*
> + * It's not entirely clear from the datasheet, but some
> + * virtual implementations don't stop until the counter
> + * is actually written.
> + */
> + if (i8253_clear_counter_on_shutdown) {
> + outb_p(0, PIT_CH0);
> + outb_p(0, PIT_CH0);
> + }
> + raw_spin_unlock(&i8253_lock);
> + }
> return false;
> + }
That's just wrong. What we want is to have the underlying problem
fixed in the driver and then make:
> clockevent_i8253_init(true);
bool clockevent_i8253_init(bool enable, bool oneshot);
so it can invoke the shutdown sequence instead of registering the pile:
if (!enable) {
shutdown();
return false;
}
...
return true;
and the call site becomes:
if (!clockevent_i8253_init(use_pit(), true))
return false;
No?
Thanks,
tglx
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