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Re: [PATCH for-4.21 01/10] x86/HPET: limit channel changes
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Fri, 17 Oct 2025 11:23:54 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Delivery-date: Fri, 17 Oct 2025 09:24:19 +0000
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On Thu, Oct 16, 2025 at 09:31:21AM +0200, Jan Beulich wrote:
> Despite 1db7829e5657 ("x86/hpet: do local APIC EOI after interrupt
> processing") we can still observe nested invocations of
> hpet_interrupt_handler(). This is, afaict, a result of previously used
> channels retaining their IRQ affinity until some other CPU re-uses them.
> Such nesting is increasingly problematic with higher CPU counts, as both
> handle_hpet_broadcast() and cpumask_raise_softirq() have a cpumask_t local
> variable. IOW already a single level of nesting may require more stack
> space (2 times above 4k) than we have available (8k), when NR_CPUS=16383
> (the maximum value presently possible).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Whether this is still worthwhile with "x86/HPET: use single, global, low-
> priority vector for broadcast IRQ" isn't quite clear to me.
Seeing the rest of the series, I don't think this is necessary
anymore? Also the comment you here is made stale by the patch that
uses a global vector.
Thanks, Roger.
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