Hi, I was talking about this patch. > From: Borislav Petkov [mailto:bp@xxxxxxxxx] > Sent: Friday, March 27, 2015 5:23 PM > Subject: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader > > From: Jiri Kosina <jkosina@xxxxxxx> > > Since GHES sources are global, we theoretically need only a single CPU > reading them per NMI instead of a thundering herd of CPUs waiting on a > spinlock in NMI context for no reason at all. > > Do that. > > Signed-off-by: Jiri Kosina <jkosina@xxxxxxx> > Signed-off-by: Borislav Petkov <bp@xxxxxxx> > --- > drivers/acpi/apei/ghes.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c > index 94a44bad5576..2bfd53cbfe80 100644 > --- a/drivers/acpi/apei/ghes.c > +++ b/drivers/acpi/apei/ghes.c > @@ -729,10 +729,10 @@ static struct llist_head ghes_estatus_llist; > static struct irq_work ghes_proc_irq_work; > > /* > - * NMI may be triggered on any CPU, so ghes_nmi_lock is used for > - * mutual exclusion. > + * NMI may be triggered on any CPU, so ghes_in_nmi is used for > + * having only one concurrent reader. > */ > -static DEFINE_RAW_SPINLOCK(ghes_nmi_lock); > +static atomic_t ghes_in_nmi = ATOMIC_INIT(0); > > static LIST_HEAD(ghes_nmi); > > @@ -840,7 +840,9 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs) > struct ghes *ghes; > int sev, ret = NMI_DONE; > > - raw_spin_lock(&ghes_nmi_lock); > + if (!atomic_add_unless(&ghes_in_nmi, 1, 1)) > + return ret; > + if (atomic_cmpxchg(&ghes_in_nmi, 0, 1)) return ret; > list_for_each_entry_rcu(ghes, &ghes_nmi, list) { > if (ghes_read_estatus(ghes, 1)) { > ghes_clear_estatus(ghes); > @@ -863,7 +865,7 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs) > #ifdef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG > irq_work_queue(&ghes_proc_irq_work); > #endif > - raw_spin_unlock(&ghes_nmi_lock); > + atomic_dec(&ghes_in_nmi); atomic_set(&ghes_in_nmi, 0); It seems most of the drivers (under drivers/) are written in this way. While the user of atomic_add_unless() is rare. Can this work for you? Thanks and best regards -Lv > return ret; > } > > -- > 2.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
