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Re: [PATCH 3/6] xen/softirq: Rework arch_skip_send_event_check() into arch_pend_softirq()


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 3 Jul 2025 10:11:23 +0200
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 03 Jul 2025 08:11:44 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 02.07.2025 16:41, Andrew Cooper wrote:
> x86 is the only architecture wanting an optimisation here, but the
> test_and_set_bit() is a store into the monitored line

Which is intentional aiui, while this reads as if this was part of the issue.

> and is racy with determining whether an IPI can be skipped.

Racy here as in limiting the effect of the optimization, but not affecting
correctness aiui: If the woken CPU managed to clear the bit already, we'd
needlessly IPI it. This could also do with saying.

Jan



 


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