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SubjectRe: [PATCH] panic: Fix panic_timeout accuracy when running on a hypervisor
On Mon, 1 Feb 2010 15:14:30 +1100
Anton Blanchard <anton@samba.org> wrote:

>
> I've had some complaints about panic_timeout being wildly innacurate on
> shared processor PowerPC partitions (a 3 minute panic_timeout taking 30
> minutes).
>
> The problem is we loop on mdelay(1) and with a 1ms in 10ms hypervisor
> timeslice each of these will take 10ms (ie 10x) longer. I expect other
> platforms with shared processor hypervisors will see the same issue.
>
> This patch keeps the old behaviour if we have a panic_blink (only keyboard
> LEDs right now) and does 1 second mdelays if we don't.
>
> ...
>
> +static void panic_blink_one_second(void)
> +{
> + static long i = 0, end;

I assumed the `static' was a brainfart and removed it?

> + if (panic_blink) {
> + end = i + MSEC_PER_SEC;
> +
> + while (i < end) {
> + i += panic_blink(i);
> + mdelay(1);
> + i++;
> + }
> + } else {
> + /*
> + * When running under a hypervisor a small mdelay may get
> + * rounded up to the hypervisor timeslice. For example, with
> + * a 1ms in 10ms hypervisor timeslice we might inflate a
> + * mdelay(1) loop by 10x.
> + *
> + * If we have nothing to blink, spin on 1 second calls to
> + * mdelay to avoid this.
> + */
> + mdelay(MSEC_PER_SEC);
> + }
> +}

In fact we can simplify it a bit:

--- a/kernel/panic.c~panic-fix-panic_timeout-accuracy-when-running-on-a-hypervisor-fix
+++ a/kernel/panic.c
@@ -42,12 +42,10 @@ EXPORT_SYMBOL(panic_blink);

static void panic_blink_one_second(void)
{
- static long i = 0, end;
-
if (panic_blink) {
- end = i + MSEC_PER_SEC;
+ long i = 0;

- while (i < end) {
+ while (i < MSEC_PER_SEC) {
i += panic_blink(i);
mdelay(1);
i++;
_
Why does it do the mdelay() as well as calling panic_blink()? hm,
because the old code did. I guess it doesn't trust panic_blink().




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