eal: customize delay function

When running single-core, some drivers tend to call rte_delay_us for a
long time, and that is causing packet drops.
To avoid this, rte_delay_us can be replaced with user-defined delay
function with:

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

When userfunc==rte_delay_us_block build-in blocking delay function is
restored.

Signed-off-by: Jozef Martiniak <jozmarti@cisco.com>

app/test/test_cycles.c

@@ -90,3 +90,48 @@ test_cycles(void)
 }
 
 REGISTER_TEST_COMMAND(cycles_autotest, test_cycles);
+
+/*
+ * rte_delay_us_callback test
+ *
+ * - check if callback is correctly registered/unregistered
+ *
+ */
+
+static unsigned int pattern;
+static void my_rte_delay_us(unsigned int us)
+{
+	pattern += us;
+}
+
+static int
+test_user_delay_us(void)
+{
+	pattern = 0;
+
+	rte_delay_us(2);
+	if (pattern != 0)
+		return -1;
+
+	/* register custom delay function */
+	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;
+
+	/* restore original delay function */
+	rte_delay_us_callback_register(rte_delay_us_block);
+
+	rte_delay_us(3);
+	if (pattern != 5)
+		return -1;
+
+	return 0;
+}
+
+REGISTER_TEST_COMMAND(user_delay_us, test_user_delay_us);

lib/librte_eal/bsdapp/eal/rte_eal_version.map

@@ -162,3 +162,11 @@ DPDK_16.07 {
 	rte_thread_setname;
 
 } DPDK_16.04;
+
+DPDK_16.11 {
+	global:
+
+	rte_delay_us_block;
+	rte_delay_us_callback_register;
+
+} DPDK_16.07;

lib/librte_eal/common/eal_common_timer.c

@@ -47,8 +47,11 @@
 /* The frequency of the RDTSC timer resolution */
 static uint64_t eal_tsc_resolution_hz;
 
+/* Pointer to user delay function */
+void (*rte_delay_us)(unsigned int) = NULL;
+
 void
-rte_delay_us(unsigned us)
+rte_delay_us_block(unsigned int us)
 {
 	const uint64_t start = rte_get_timer_cycles();
 	const uint64_t ticks = (uint64_t)us * rte_get_timer_hz() / 1E6;
@@ -84,3 +87,15 @@ 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 int))
+{
+	rte_delay_us = userfunc;
+}
+
+static void __attribute__((constructor))
+rte_timer_init(void)
+{
+	/* set rte_delay_us_block as a delay function */
+	rte_delay_us_callback_register(rte_delay_us_block);
+}

lib/librte_eal/common/include/generic/rte_cycles.h

@@ -180,15 +180,16 @@ rte_get_timer_hz(void)
 	default: rte_panic("Invalid timer source specified\n");
 	}
 }
-
 /**
  * Wait at least us microseconds.
+ * This function can be replaced with user-defined function.
+ * @see rte_delay_us_callback_register
  *
  * @param us
  *   The number of microseconds to wait.
  */
 void
-rte_delay_us(unsigned us);
+(*rte_delay_us)(unsigned int us);
 
 /**
  * Wait at least ms milliseconds.
@@ -202,4 +203,21 @@ rte_delay_ms(unsigned ms)
 	rte_delay_us(ms * 1000);
 }
 
+/**
+ * Blocking delay function.
+ *
+ * @param us
+ *   Number of microseconds to wait.
+ */
+void rte_delay_us_block(unsigned int us);
+
+/**
+ * Replace rte_delay_us with user defined function.
+ *
+ * @param userfunc
+ *   User function which replaces rte_delay_us. rte_delay_us_block restores
+ *   buildin block delay function.
+ */
+void rte_delay_us_callback_register(void(*userfunc)(unsigned int));
+
 #endif /* _RTE_CYCLES_H_ */

lib/librte_eal/linuxapp/eal/rte_eal_version.map

@@ -166,3 +166,11 @@ DPDK_16.07 {
 	rte_thread_setname;
 
 } DPDK_16.04;
+
+DPDK_16.11 {
+	global:
+
+	rte_delay_us_block;
+	rte_delay_us_callback_register;
+
+} DPDK_16.07;