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Subject[PATCH v3 6/8] xen/events: add per-xenbus device event statistics and settings
Date
Add syfs nodes for each xenbus device showing event statistics (number
of events and spurious events, number of associated event channels)
and for setting a spurious event threshold in case a frontend is
sending too many events without being rogue on purpose.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
V2:
- add documentation (Boris Ostrovsky)
---
.../ABI/testing/sysfs-devices-xenbus | 41 ++++++++++++
drivers/xen/events/events_base.c | 27 +++++++-
drivers/xen/xenbus/xenbus_probe.c | 66 +++++++++++++++++++
include/xen/xenbus.h | 7 ++
4 files changed, 139 insertions(+), 2 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-devices-xenbus

diff --git a/Documentation/ABI/testing/sysfs-devices-xenbus b/Documentation/ABI/testing/sysfs-devices-xenbus
new file mode 100644
index 000000000000..fd796cb4f315
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-xenbus
@@ -0,0 +1,41 @@
+What: /sys/devices/*/xenbus/event_channels
+Date: February 2021
+Contact: Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+ Number of Xen event channels associated with a kernel based
+ paravirtualized device frontend or backend.
+
+What: /sys/devices/*/xenbus/events
+Date: February 2021
+Contact: Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+ Total number of Xen events received for a Xen pv device
+ frontend or backend.
+
+What: /sys/devices/*/xenbus/jiffies_eoi_delayed
+Date: February 2021
+Contact: Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+ Summed up time in jiffies the EOI of an interrupt for a Xen
+ pv device has been delayed in order to avoid stalls due to
+ event storms. This value rising is a first sign for a rogue
+ other end of the pv device.
+
+What: /sys/devices/*/xenbus/spurious_events
+Date: February 2021
+Contact: Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+ Number of events received for a Xen pv device which did not
+ require any action. Too many spurious events in a row will
+ trigger delayed EOI processing.
+
+What: /sys/devices/*/xenbus/spurious_threshold
+Date: February 2021
+Contact: Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+ Controls the tolerated number of subsequent spurious events
+ before delayed EOI processing is triggered for a Xen pv
+ device. Default is 1. This can be modified in case the other
+ end of the pv device is issuing spurious events on a regular
+ basis and is known not to be malicious on purpose. Raising
+ the value for such cases can improve pv device performance.
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index b60df189ecbc..a3636fb03417 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -332,6 +332,8 @@ static int xen_irq_info_evtchn_setup(unsigned irq,

ret = xen_irq_info_common_setup(info, irq, IRQT_EVTCHN, evtchn, 0);
info->u.interdomain = dev;
+ if (dev)
+ atomic_inc(&dev->event_channels);

return ret;
}
@@ -606,18 +608,28 @@ static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious)
return;

if (spurious) {
+ struct xenbus_device *dev = info->u.interdomain;
+ unsigned int threshold = 1;
+
+ if (dev && dev->spurious_threshold)
+ threshold = dev->spurious_threshold;
+
if ((1 << info->spurious_cnt) < (HZ << 2)) {
if (info->spurious_cnt != 0xFF)
info->spurious_cnt++;
}
- if (info->spurious_cnt > 1) {
- delay = 1 << (info->spurious_cnt - 2);
+ if (info->spurious_cnt > threshold) {
+ delay = 1 << (info->spurious_cnt - 1 - threshold);
if (delay > HZ)
delay = HZ;
if (!info->eoi_time)
info->eoi_cpu = smp_processor_id();
info->eoi_time = get_jiffies_64() + delay;
+ if (dev)
+ atomic_add(delay, &dev->jiffies_eoi_delayed);
}
+ if (dev)
+ atomic_inc(&dev->spurious_events);
} else {
info->spurious_cnt = 0;
}
@@ -954,6 +966,7 @@ static void __unbind_from_irq(unsigned int irq)

if (VALID_EVTCHN(evtchn)) {
unsigned int cpu = cpu_from_irq(irq);
+ struct xenbus_device *dev;

xen_evtchn_close(evtchn);

@@ -964,6 +977,11 @@ static void __unbind_from_irq(unsigned int irq)
case IRQT_IPI:
per_cpu(ipi_to_irq, cpu)[ipi_from_irq(irq)] = -1;
break;
+ case IRQT_EVTCHN:
+ dev = info->u.interdomain;
+ if (dev)
+ atomic_dec(&dev->event_channels);
+ break;
default:
break;
}
@@ -1627,6 +1645,7 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl)
{
int irq;
struct irq_info *info;
+ struct xenbus_device *dev;

irq = get_evtchn_to_irq(port);
if (irq == -1)
@@ -1658,6 +1677,10 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl)
if (xchg_acquire(&info->is_active, 1))
return;

+ dev = (info->type == IRQT_EVTCHN) ? info->u.interdomain : NULL;
+ if (dev)
+ atomic_inc(&dev->events);
+
if (ctrl->defer_eoi) {
info->eoi_cpu = smp_processor_id();
info->irq_epoch = __this_cpu_read(irq_epoch);
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 8a75092bb148..97f0d234482d 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -206,6 +206,65 @@ void xenbus_otherend_changed(struct xenbus_watch *watch,
}
EXPORT_SYMBOL_GPL(xenbus_otherend_changed);

+#define XENBUS_SHOW_STAT(name) \
+static ssize_t show_##name(struct device *_dev, \
+ struct device_attribute *attr, \
+ char *buf) \
+{ \
+ struct xenbus_device *dev = to_xenbus_device(_dev); \
+ \
+ return sprintf(buf, "%d\n", atomic_read(&dev->name)); \
+} \
+static DEVICE_ATTR(name, 0444, show_##name, NULL)
+
+XENBUS_SHOW_STAT(event_channels);
+XENBUS_SHOW_STAT(events);
+XENBUS_SHOW_STAT(spurious_events);
+XENBUS_SHOW_STAT(jiffies_eoi_delayed);
+
+static ssize_t show_spurious_threshold(struct device *_dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct xenbus_device *dev = to_xenbus_device(_dev);
+
+ return sprintf(buf, "%d\n", dev->spurious_threshold);
+}
+
+static ssize_t set_spurious_threshold(struct device *_dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct xenbus_device *dev = to_xenbus_device(_dev);
+ unsigned int val;
+ ssize_t ret;
+
+ ret = kstrtouint(buf, 0, &val);
+ if (ret)
+ return ret;
+
+ dev->spurious_threshold = val;
+
+ return count;
+}
+
+static DEVICE_ATTR(spurious_threshold, 0644, show_spurious_threshold,
+ set_spurious_threshold);
+
+static struct attribute *xenbus_attrs[] = {
+ &dev_attr_event_channels.attr,
+ &dev_attr_events.attr,
+ &dev_attr_spurious_events.attr,
+ &dev_attr_jiffies_eoi_delayed.attr,
+ &dev_attr_spurious_threshold.attr,
+ NULL
+};
+
+static const struct attribute_group xenbus_group = {
+ .name = "xenbus",
+ .attrs = xenbus_attrs,
+};
+
int xenbus_dev_probe(struct device *_dev)
{
struct xenbus_device *dev = to_xenbus_device(_dev);
@@ -253,6 +312,11 @@ int xenbus_dev_probe(struct device *_dev)
return err;
}

+ dev->spurious_threshold = 1;
+ if (sysfs_create_group(&dev->dev.kobj, &xenbus_group))
+ dev_warn(&dev->dev, "sysfs_create_group on %s failed.\n",
+ dev->nodename);
+
return 0;
fail_put:
module_put(drv->driver.owner);
@@ -269,6 +333,8 @@ int xenbus_dev_remove(struct device *_dev)

DPRINTK("%s", dev->nodename);

+ sysfs_remove_group(&dev->dev.kobj, &xenbus_group);
+
free_otherend_watch(dev);

if (drv->remove) {
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index bf3cfc7c35d0..0b1386073d49 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -88,6 +88,13 @@ struct xenbus_device {
struct completion down;
struct work_struct work;
struct semaphore reclaim_sem;
+
+ /* Event channel based statistics and settings. */
+ atomic_t event_channels;
+ atomic_t events;
+ atomic_t spurious_events;
+ atomic_t jiffies_eoi_delayed;
+ unsigned int spurious_threshold;
};

static inline struct xenbus_device *to_xenbus_device(struct device *dev)
--
2.26.2
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