Messages in this thread | | | Date | Mon, 9 Jan 2023 08:59:42 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH x86/nmi 1/2] x86/nmi: Accumulate NMI-progress evidence in exc_nmi() |
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On Mon, Jan 09, 2023 at 05:19:59PM +0100, Peter Zijlstra wrote: > On Wed, Jan 04, 2023 at 05:15:36PM -0800, Paul E. McKenney wrote: > > > diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c > > index cec0bfa3bc04f..4f1651dc65b3a 100644 > > --- a/arch/x86/kernel/nmi.c > > +++ b/arch/x86/kernel/nmi.c > > @@ -69,6 +69,15 @@ struct nmi_stats { > > unsigned int unknown; > > unsigned int external; > > unsigned int swallow; > > + unsigned long recv_jiffies; > > + unsigned long idt_seq; > > + unsigned long idt_nmi_seq; > > + unsigned long idt_ignored; > > + atomic_long_t idt_calls; > > + unsigned long idt_seq_snap; > > + unsigned long idt_nmi_seq_snap; > > + unsigned long idt_ignored_snap; > > + long idt_calls_snap; > > }; > > Urgh, this is more than a whole cacheline of extra data :/ Can't we make > this #ifdef CONFIG_NMI_CHECK_CPU ?
We can. However, the new data is at the end of the structure. Plus doing that will also require converting the IS_ENABLED() checks to #ifdef or to lots of tiny functions, neither of which will be at all pretty.
Another approach would be to have a #else that created a union of all of these fields, thus reducing this unused space so that of a single unsigned long, while still permitting IS_ENABLED() checks. Thoughts?
> > @@ -509,8 +526,15 @@ DEFINE_IDTENTRY_RAW(exc_nmi) > > > > inc_irq_stat(__nmi_count); > > > > - if (!ignore_nmis) > > + if (IS_ENABLED(CONFIG_NMI_CHECK_CPU) && ignore_nmis) { > > + WRITE_ONCE(nsp->idt_ignored, nsp->idt_ignored + 1); > > + } else if (!ignore_nmis) { > > + WRITE_ONCE(nsp->idt_nmi_seq, nsp->idt_nmi_seq + 1); > > + WARN_ON_ONCE(!(nsp->idt_nmi_seq & 0x1)); > > default_do_nmi(regs); > > + WRITE_ONCE(nsp->idt_nmi_seq, nsp->idt_nmi_seq + 1); > > + WARN_ON_ONCE(nsp->idt_nmi_seq & 0x1); > > + } > > > > irqentry_nmi_exit(regs, irq_state); > > That is not a NO-OP when !CONFIG_NMI_CHECK_CPU :/
Good catch, will fix!
Thanx, Paul
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