itrace: Add documentation for itrace

ascend inclusion
category: feature
bugzilla: NA
CVE: NA

---------------------------------------------

Add documentation for itrace.
Signed-off-by: NBixuan Cui <cuibixuan@huawei.com>
Reviewed-by: NDing Tianhong <dingtianhong@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

Documentation/trace/index.rst

@@ -22,3 +22,4 @@ Linux Tracing Technologies
    hwlat_detector
    intel_th
    stm
+   itrace

Documentation/trace/itrace.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Interrupts Tracing
+=============
+
+:Author: Bixuan Cui
+
+1. Introduction
+===============
+
+Itrace (Interrupt Tracing) is a lightweight interrupt tracing tool. It supports
+the following functions:
+
+* Ihandler(Interrupt Handler) tracer can trace and calculate the time consumed of
+  the hardware irq function and list the name, number and duration of the interrupt.
+
+* Irqsoff tracer can trace the areas that disable interrupts.
+
+* Ihandler and Irqsoff support dynamic disable and threshold setting.
+
+2. Using Ihandler Tracing
+======================
+
+2.1 Enable Ihandler Tracing
+---------------------------------
+
+Echo threshold val to /proc/irq/itrace_ihandler to enable ihandler tracer. The
+threshold value ranges from 1 to 10000000, in microsecond. For example::
+
+        # echo 20 > /proc/irq/itrace_ihandler
+
+Cat /proc/irq/itrace_ihandler to get the message of ihandler. For example::
+
+        # echo 1 > /proc/irq/itrace_ihandler
+        # cat /proc/irq/itrace_ihandler
+        [irq_handler CPU0]:
+          irq:14 name:uart-pl011 max_time:8(us) count:278
+          irq:31 name:ufshcd max_time:44(us) count:1684
+          irq:565 name:mailbox-1-lp-rx-acp max_time:6(us) count:10
+          irq:602 name:devdrv-functional_c max_time:1(us) count:1
+
+Note: Only the captured information is displayed. Five lines for each cpu
+      by default.
+
+2.2 Disable Ihandler Tracing
+---------------------------------
+
+Echo 0 to /proc/irq/itrace_ihandler to disable ihandler tracer. For example::
+
+        # echo 0 > /proc/irq/itrace_ihandler
+
+2.3 Set the number of displayed
+---------------------------------
+
+Echo num to /proc/irq/itrace_ihandler_num to set the number of displayed. The
+num value ranges from 1 to 30. For example::
+
+        # echo 20 > /proc/irq/itrace_ihandler_num
+
+3. Using Irqsoff Tracing
+======================
+
+3.1 Enable Irqsoff Tracing
+---------------------------------
+
+Echo threshold val to /proc/irq/itrace_irqsoff to enable irqsoff tracer. The
+threshold value ranges from 1 to 10000000, in microsecond. For example::
+
+        # echo 20 > /proc/irq/itrace_irqsoff
+
+Cat /proc/irq/itrace_irqsoff to get the message of irqsoff. For example::
+
+        # echo 1 > /proc/irq/itrace_irqsoff
+        # cat /proc/irq/itrace_irqsoff
+        [irqsoff CPU0]:
+          max_time:3(us) caller:__do_softirq+0x94/0x328
+          max_time:4(us) caller:__do_softirq+0x94/0x328
+          max_time:4(us) caller:__do_softirq+0x94/0x328
+        [irqsoff CPU1]:
+          max_time:2(us) caller:finish_task_switch+0x6c/0x1e0
+          max_time:1(us) caller:__arm64_sys_setpgid+0xd0/0x1d8
+          max_time:2(us) caller:pagevec_lru_move_fn+0x18c/0x1c8
+        [irqsoff CPU2]:
+          max_time:4(us) caller:__do_softirq+0x94/0x328
+          max_time:6(us) caller:__do_softirq+0x94/0x328
+          max_time:2(us) caller:rcu_idle_exit+0xa4/0xd8
+        [irqsoff CPU3]:
+          max_time:3(us) caller:rcu_idle_exit+0xa4/0xd8
+          max_time:1(us) caller:__do_softirq+0x94/0x328
+          max_time:2(us) caller:osal_spin_unlock_irqrestore+0x5c/0x80 [drv_osal]
+
+Note: Only the captured information is displayed. Three lines for each cpu
+      by default.
+
+3.2 Disable Irqsoff Tracing
+---------------------------------
+
+Echo 0 to /proc/irq/itrace_irqsoff to disable irqsoff tracer. For example::
+
+        # echo 0 > /proc/irq/itrace_irqsoff
+
+3.3 Set the number of displayed
+---------------------------------
+
+Echo num to /proc/irq/itrace_irqsoff_num to set the number of displayed.
+The num value ranges from 1 to 30. For example::
+
+        # echo 20 > /proc/irq/itrace_irqsoff_num