genirq: Avoid summation loops for /proc/stat

[ Upstream commit 1136b0728969901a091f0471968b2b76ed14d9ad ]

Waiman reported that on large systems with a large amount of interrupts the
readout of /proc/stat takes a long time to sum up the interrupt
statistics. In principle this is not a problem. but for unknown reasons
some enterprise quality software reads /proc/stat with a high frequency.

The reason for this is that interrupt statistics are accounted per cpu. So
the /proc/stat logic has to sum up the interrupt stats for each interrupt.

This can be largely avoided for interrupts which are not marked as
'PER_CPU' interrupts by simply adding a per interrupt summation counter
which is incremented along with the per interrupt per cpu counter.

The PER_CPU interrupts need to avoid that and use only per cpu accounting
because they share the interrupt number and the interrupt descriptor and
concurrent updates would conflict or require unwanted synchronization.

Reported-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Daniel Colascione <dancol@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: https://lkml.kernel.org/r/20190208135020.925487496@linutronix.de
8<-------------

v2: Undo the unintentional layout change of struct irq_desc.

 include/linux/irqdesc.h |    1 +
 kernel/irq/chip.c       |   12 ++++++++++--
 kernel/irq/internals.h  |    8 +++++++-
 kernel/irq/irqdesc.c    |    7 ++++++-
 4 files changed, 24 insertions(+), 4 deletions(-)

Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index c9be57931b58110dd3f7af4f7e059b28bce4843c..bb5547a83daf54cd3c32098bc5ec6b01509c8468 100644 (file)
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -61,6 +61,7 @@ struct irq_desc {
        unsigned int            core_internal_state__do_not_mess_with_it;
        unsigned int            depth;          /* nested irq disables */
        unsigned int            wake_depth;     /* nested wake enables */
+       unsigned int            tot_count;
        unsigned int            irq_count;      /* For detecting broken IRQs */
        unsigned long           last_unhandled; /* Aging timer for unhandled count */
        unsigned int            irqs_unhandled;

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index f30110e1b8c9a9739ff137c099c1465a66c9eb39..9e745cc0726d6771ae0a78a79751d458764e4896 100644 (file)
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -729,7 +729,11 @@ void handle_percpu_irq(struct irq_desc *desc)
 {
        struct irq_chip *chip = irq_desc_get_chip(desc);
 
-       kstat_incr_irqs_this_cpu(desc);
+       /*
+        * PER CPU interrupts are not serialized. Do not touch
+        * desc->tot_count.
+        */
+       __kstat_incr_irqs_this_cpu(desc);
 
        if (chip->irq_ack)
                chip->irq_ack(&desc->irq_data);
@@ -758,7 +762,11 @@ void handle_percpu_devid_irq(struct irq_desc *desc)
        unsigned int irq = irq_desc_get_irq(desc);
        irqreturn_t res;
 
-       kstat_incr_irqs_this_cpu(desc);
+       /*
+        * PER CPU interrupts are not serialized. Do not touch
+        * desc->tot_count.
+        */
+       __kstat_incr_irqs_this_cpu(desc);
 
        if (chip->irq_ack)
                chip->irq_ack(&desc->irq_data);

diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index bc226e783bd236b1e1a98a523deef673b7d56635..22e3f29a30d8b362c5785a2f9db73895a974a666 100644 (file)
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -199,12 +199,18 @@ static inline bool irqd_has_set(struct irq_data *d, unsigned int mask)
 
 #undef __irqd_to_state
 
-static inline void kstat_incr_irqs_this_cpu(struct irq_desc *desc)
+static inline void __kstat_incr_irqs_this_cpu(struct irq_desc *desc)
 {
        __this_cpu_inc(*desc->kstat_irqs);
        __this_cpu_inc(kstat.irqs_sum);
 }
 
+static inline void kstat_incr_irqs_this_cpu(struct irq_desc *desc)
+{
+       __kstat_incr_irqs_this_cpu(desc);
+       desc->tot_count++;
+}
+
 static inline int irq_desc_get_node(struct irq_desc *desc)
 {
        return irq_common_data_get_node(&desc->irq_common_data);

diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 77977f55dff7166329b1886efd1d7a163bf850a7..5e0ea17d01a6507493abaa1ee8cd2e404b47ac5d 100644 (file)
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -109,6 +109,7 @@ static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node,
        desc->depth = 1;
        desc->irq_count = 0;
        desc->irqs_unhandled = 0;
+       desc->tot_count = 0;
        desc->name = NULL;
        desc->owner = owner;
        for_each_possible_cpu(cpu)
@@ -880,11 +881,15 @@ unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
 unsigned int kstat_irqs(unsigned int irq)
 {
        struct irq_desc *desc = irq_to_desc(irq);
-       int cpu;
        unsigned int sum = 0;
+       int cpu;
 
        if (!desc || !desc->kstat_irqs)
                return 0;
+       if (!irq_settings_is_per_cpu_devid(desc) &&
+           !irq_settings_is_per_cpu(desc))
+           return desc->tot_count;
+
        for_each_possible_cpu(cpu)
                sum += *per_cpu_ptr(desc->kstat_irqs, cpu);
        return sum;