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

[jozmarti at cisco.com]

From: Jozef Martiniak <jozmarti at cisco.com>

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==NULL, build-in blocking delay function is restored.

Signed-off-by: Jozef Martiniak <jozmarti at cisco.com>
---
 app/test/test_cycles.c                             | 45 ++++++++++++++++++++++
 lib/librte_eal/bsdapp/eal/rte_eal_version.map      |  7 ++++
 lib/librte_eal/common/eal_common_timer.c           | 22 ++++++++++-
 lib/librte_eal/common/include/generic/rte_cycles.h | 15 +++++++-
 lib/librte_eal/linuxapp/eal/rte_eal_version.map    |  7 ++++
 5 files changed, 93 insertions(+), 3 deletions(-)

diff --git a/app/test/test_cycles.c b/app/test/test_cycles.c
index f6c043a..7415ac8 100644
--- a/app/test/test_cycles.c
+++ b/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 int pattern;
+static void my_rte_delay_us(unsigned 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(NULL);
+
+    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/bsdapp/eal/rte_eal_version.map b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
index a335e04..2f83ed0 100644
--- a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
+++ b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
@@ -162,3 +162,10 @@ DPDK_16.07 {
 	rte_thread_setname;
 
 } DPDK_16.04;
+
+DPDK_16.11 {
+	global:
+
+	rte_delay_us_callback_register;
+
+} DPDK_16.07;
diff --git a/lib/librte_eal/common/eal_common_timer.c b/lib/librte_eal/common/eal_common_timer.c
index c4227cd..ddfa9d1 100644
--- a/lib/librte_eal/common/eal_common_timer.c
+++ b/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;
 
-void
-rte_delay_us(unsigned us)
+/* Pointer to user delay function */
+void (*rte_delay_us)(unsigned) = NULL;
+
+static void
+rte_delay_us_block(unsigned us)
 {
 	const uint64_t start = rte_get_timer_cycles();
 	const uint64_t ticks = (uint64_t)us * rte_get_timer_hz() / 1E6;
@@ -84,3 +87,18 @@ 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))
+{
+    if (userfunc == NULL)
+        rte_delay_us = rte_delay_us_block;
+    else
+        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(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..7a45b58 100644
--- a/lib/librte_eal/common/include/generic/rte_cycles.h
+++ b/lib/librte_eal/common/include/generic/rte_cycles.h
@@ -182,13 +182,16 @@ rte_get_timer_hz(void)
 }
 
 /**
+ *
  * Wait at least us microseconds.
+ * This function can be replaced with user-defined function using
+ * rte_delay_us_callback_register
  *
  * @param us
  *   The number of microseconds to wait.
  */
 void
-rte_delay_us(unsigned us);
+(*rte_delay_us)(unsigned us);
 
 /**
  * Wait at least ms milliseconds.
@@ -202,4 +205,14 @@ 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. NULL restores
+ *   buildin block delay function.
+ */
+void rte_delay_us_callback_register(void(*userfunc)(unsigned));
+
+
 #endif /* _RTE_CYCLES_H_ */
diff --git a/lib/librte_eal/linuxapp/eal/rte_eal_version.map b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
index db8c984..4ba30ed 100644
--- a/lib/librte_eal/linuxapp/eal/rte_eal_version.map
+++ b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
@@ -166,3 +166,10 @@ DPDK_16.07 {
 	rte_thread_setname;
 
 } DPDK_16.04;
+
+DPDK_16.11 {
+	global:
+
+	rte_delay_us_callback_register;
+
+} DPDK_16.07;
-- 
2.1.4