Now that we have everything in a C file, we can store the information
about our sleep, and have a native mechanism to wake up the sleeping
core. This mechanism would however only wake up a core that's sleeping
while monitoring - waking up from `rte_power_pause` won't work.
Signed-off-by: Anatoly Burakov <anatoly.bura...@intel.com>
---
Notes:
v13:
- Add comments around wakeup code to explain what it does
- Add lcore_id parameter checking to prevent buffer overrun
lib/librte_eal/arm/rte_power_intrinsics.c | 9 ++
.../include/generic/rte_power_intrinsics.h | 16 ++++
lib/librte_eal/ppc/rte_power_intrinsics.c | 9 ++
lib/librte_eal/version.map | 1 +
lib/librte_eal/x86/rte_power_intrinsics.c | 85 +++++++++++++++++++
5 files changed, 120 insertions(+)
diff --git a/lib/librte_eal/arm/rte_power_intrinsics.c
b/lib/librte_eal/arm/rte_power_intrinsics.c
index 6b8219b919..14081a2c5b 100644
--- a/lib/librte_eal/arm/rte_power_intrinsics.c
+++ b/lib/librte_eal/arm/rte_power_intrinsics.c
@@ -23,3 +23,12 @@ rte_power_pause(const uint64_t tsc_timestamp)
{
RTE_SET_USED(tsc_timestamp);
}
+
+/**
+ * This function is not supported on ARM.
+ */
+void
+rte_power_monitor_wakeup(const unsigned int lcore_id)
+{
+ RTE_SET_USED(lcore_id);
+}
diff --git a/lib/librte_eal/include/generic/rte_power_intrinsics.h
b/lib/librte_eal/include/generic/rte_power_intrinsics.h
index a6f1955996..e311d6f8ea 100644
--- a/lib/librte_eal/include/generic/rte_power_intrinsics.h
+++ b/lib/librte_eal/include/generic/rte_power_intrinsics.h
@@ -57,6 +57,22 @@ __rte_experimental
void rte_power_monitor(const struct rte_power_monitor_cond *pmc,
const uint64_t tsc_timestamp);
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice
+ *
+ * Wake up a specific lcore that is in a power optimized state and is
monitoring
+ * an address.
+ *
+ * @note This function will *not* wake up a core that is in a power optimized
+ * state due to calling `rte_power_pause`.
+ *
+ * @param lcore_id
+ * Lcore ID of a sleeping thread.
+ */
+__rte_experimental
+void rte_power_monitor_wakeup(const unsigned int lcore_id);
+
/**
* @warning
* @b EXPERIMENTAL: this API may change without prior notice
diff --git a/lib/librte_eal/ppc/rte_power_intrinsics.c
b/lib/librte_eal/ppc/rte_power_intrinsics.c
index 9a40c4d5d6..a7db61a7c3 100644
--- a/lib/librte_eal/ppc/rte_power_intrinsics.c
+++ b/lib/librte_eal/ppc/rte_power_intrinsics.c
@@ -23,3 +23,12 @@ rte_power_pause(const uint64_t tsc_timestamp)
{
RTE_SET_USED(tsc_timestamp);
}
+
+/**
+ * This function is not supported on PPC64.
+ */
+void
+rte_power_monitor_wakeup(const unsigned int lcore_id)
+{
+ RTE_SET_USED(lcore_id);
+}
diff --git a/lib/librte_eal/version.map b/lib/librte_eal/version.map
index 20945b1efa..ac026e289d 100644
--- a/lib/librte_eal/version.map
+++ b/lib/librte_eal/version.map
@@ -406,6 +406,7 @@ EXPERIMENTAL {
# added in 21.02
rte_power_monitor;
+ rte_power_monitor_wakeup;
rte_power_pause;
};
diff --git a/lib/librte_eal/x86/rte_power_intrinsics.c
b/lib/librte_eal/x86/rte_power_intrinsics.c
index 487a783a2c..941da138ce 100644
--- a/lib/librte_eal/x86/rte_power_intrinsics.c
+++ b/lib/librte_eal/x86/rte_power_intrinsics.c
@@ -2,8 +2,31 @@
* Copyright(c) 2020 Intel Corporation
*/
+#include <rte_common.h>
+#include <rte_lcore.h>
+#include <rte_spinlock.h>
+
#include "rte_power_intrinsics.h"
+/*
+ * Per-lcore structure holding current status of C0.2 sleeps.
+ */
+static struct power_wait_status {
+ rte_spinlock_t lock;
+ volatile void *monitor_addr; /**< NULL if not currently sleeping */
+} __rte_cache_aligned wait_status[RTE_MAX_LCORE];
+
+static inline void
+__umwait_wakeup(volatile void *addr)
+{
+ uint64_t val;
+
+ /* trigger a write but don't change the value */
+ val = __atomic_load_n((volatile uint64_t *)addr, __ATOMIC_RELAXED);
+ __atomic_compare_exchange_n((volatile uint64_t *)addr, &val, val, 0,
+ __ATOMIC_RELAXED, __ATOMIC_RELAXED);
+}
+
static bool wait_supported;
static inline uint64_t
@@ -36,6 +59,12 @@ rte_power_monitor(const struct rte_power_monitor_cond *pmc,
{
const uint32_t tsc_l = (uint32_t)tsc_timestamp;
const uint32_t tsc_h = (uint32_t)(tsc_timestamp >> 32);
+ const unsigned int lcore_id = rte_lcore_id();
+ struct power_wait_status *s;
+
+ /* prevent non-EAL thread from using this API */
+ if (lcore_id >= RTE_MAX_LCORE)
+ return;
/* prevent user from running this instruction if it's not supported */
if (!wait_supported)
@@ -60,11 +89,24 @@ rte_power_monitor(const struct rte_power_monitor_cond *pmc,
if (masked == pmc->val)
return;
}
+
+ s = &wait_status[lcore_id];
+
+ /* update sleep address */
+ rte_spinlock_lock(&s->lock);
+ s->monitor_addr = pmc->addr;
+ rte_spinlock_unlock(&s->lock);
+
/* execute UMWAIT */
asm volatile(".byte 0xf2, 0x0f, 0xae, 0xf7;"
: /* ignore rflags */
: "D"(0), /* enter C0.2 */
"a"(tsc_l), "d"(tsc_h));
+
+ /* erase sleep address */
+ rte_spinlock_lock(&s->lock);
+ s->monitor_addr = NULL;
+ rte_spinlock_unlock(&s->lock);
}
/**
@@ -97,3 +139,46 @@ RTE_INIT(rte_power_intrinsics_init) {
if (i.power_monitor && i.power_pause)
wait_supported = 1;
}
+
+void
+rte_power_monitor_wakeup(const unsigned int lcore_id)
+{
+ struct power_wait_status *s;
+
+ /* prevent buffer overrun */
+ if (lcore_id >= RTE_MAX_LCORE)
+ return;
+
+ /* prevent user from running this instruction if it's not supported */
+ if (!wait_supported)
+ return;
+
+ s = &wait_status[lcore_id];
+
+ /*
+ * There is a race condition between sleep, wakeup and locking, but we
+ * don't need to handle it.
+ *
+ * Possible situations:
+ *
+ * 1. T1 locks, sets address, unlocks
+ * 2. T2 locks, triggers wakeup, unlocks
+ * 3. T1 sleeps
+ *
+ * In this case, because T1 has already set the address for monitoring,
+ * we will wake up immediately even if T2 triggers wakeup before T1
+ * goes to sleep.
+ *
+ * 1. T1 locks, sets address, unlocks, goes to sleep, and wakes up
+ * 2. T2 locks, triggers wakeup, and unlocks
+ * 3. T1 locks, erases address, and unlocks
+ *
+ * In this case, since we've already woken up, the "wakeup" was
+ * unneeded, and since T1 is still waiting on T2 releasing the lock, the
+ * wakeup address is still valid so it's perfectly safe to write it.
+ */
+ rte_spinlock_lock(&s->lock);
+ if (s->monitor_addr != NULL)
+ __umwait_wakeup(s->monitor_addr);
+ rte_spinlock_unlock(&s->lock);
+}
--
2.25.1
