[dpdk-dev] [PATCH] rte_delay_us can be replaced with user function

[jozmarti@cisco.com]

From: Jozef Martiniak <jozmarti@cisco.com>

when running single-core, some drivers tend to call rte_delay_us for a
long time, and that is causing packet drops.
Attached patch introduces 2 new functions:

void rte_delay_us_callback_register(void(*userfunc)(unsigned));
void rte_delay_us_callback_unregister(void);

First one replaces rte_delay_us with userfunc and second one restores
original rte_delay_us.
Test user_delay_us is included.

Signed-off-by: Jozef Martiniak <jozmarti@cisco.com>
---
 app/test/test_cycles.c                             | 39 ++++++++++++++++++++++
 lib/librte_eal/common/eal_common_timer.c           | 19 +++++++++++
 lib/librte_eal/common/include/generic/rte_cycles.h | 13 ++++++++
 3 files changed, 71 insertions(+)

diff --git a/app/test/test_cycles.c b/app/test/test_cycles.c
index f6c043a..2b44a53 100644
--- a/app/test/test_cycles.c
+++ b/app/test/test_cycles.c
@@ -90,3 +90,42 @@ test_cycles(void)
 }
 
 REGISTER_TEST_COMMAND(cycles_autotest, test_cycles);
+
+/*
+ * rte_delay_us_callback test
+ *
+ * - check if callback is correctly registered/unregistered
+ *
+ */
+
+static int pattern;
+static void my_rte_delay_us(unsigned us)
+{
+    pattern += us;
+}
+
+static int
+test_user_delay_us(void)
+{
+    pattern = 0;
+
+    rte_delay_us_callback_register(my_rte_delay_us);
+
+    rte_delay_us(2);
+    if (pattern != 2)
+        return -1;
+
+    rte_delay_us(3);
+    if (pattern != 5)
+        return -1;
+
+    rte_delay_us_callback_unregister();
+
+    rte_delay_us(3);
+    if (pattern != 5)
+        return -1;
+
+    return 0;
+}
+
+REGISTER_TEST_COMMAND(user_delay_us, test_user_delay_us);
diff --git a/lib/librte_eal/common/eal_common_timer.c b/lib/librte_eal/common/eal_common_timer.c
index c4227cd..a982562 100644
--- a/lib/librte_eal/common/eal_common_timer.c
+++ b/lib/librte_eal/common/eal_common_timer.c
@@ -47,9 +47,18 @@
 /* The frequency of the RDTSC timer resolution */
 static uint64_t eal_tsc_resolution_hz;
 
+/* User function which replaces rte_delay_us function */
+static void (*rte_delay_us_override)(unsigned) = NULL;
+
 void
 rte_delay_us(unsigned us)
 {
+	if (unlikely(rte_delay_us_override != NULL))
+	{
+	    rte_delay_us_override(us);
+	    return;
+	}
+
 	const uint64_t start = rte_get_timer_cycles();
 	const uint64_t ticks = (uint64_t)us * rte_get_timer_hz() / 1E6;
 	while ((rte_get_timer_cycles() - start) < ticks)
@@ -84,3 +93,13 @@ set_tsc_freq(void)
 	RTE_LOG(DEBUG, EAL, "TSC frequency is ~%" PRIu64 " KHz\n", freq / 1000);
 	eal_tsc_resolution_hz = freq;
 }
+
+void rte_delay_us_callback_register(void (*userfunc)(unsigned))
+{
+    rte_delay_us_override = userfunc;
+}
+
+void rte_delay_us_callback_unregister(void)
+{
+    rte_delay_us_override = NULL;
+}
diff --git a/lib/librte_eal/common/include/generic/rte_cycles.h b/lib/librte_eal/common/include/generic/rte_cycles.h
index 8cc21f2..274f798 100644
--- a/lib/librte_eal/common/include/generic/rte_cycles.h
+++ b/lib/librte_eal/common/include/generic/rte_cycles.h
@@ -202,4 +202,17 @@ rte_delay_ms(unsigned ms)
 	rte_delay_us(ms * 1000);
 }
 
+/**
+ * Replace rte_delay_us with user defined function.
+ *
+ * @param userfunc
+ *   User function which replaces rte_delay_us.
+ */
+void rte_delay_us_callback_register(void(*userfunc)(unsigned));
+
+/**
+ * Unregister user callback function. Restores original rte_delay_us.
+ */
+void rte_delay_us_callback_unregister(void);
+
 #endif /* _RTE_CYCLES_H_ */
-- 
2.1.4