wu-sheng commented on code in PR #614:
URL:
https://github.com/apache/skywalking-website/pull/614#discussion_r1241199891
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content/blog/2023-06-25-intruducing-continuous-profiling-skywalking-with-ebpf/index.md:
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+---
+title: "Activating Automatical Performance Analysis -- Continuous Profiling"
+date: 2023-06-25
+author: "Han Liu"
+description: "Introduce and demonstrate how SkyWalking implements eBPF-based
process monitoring with few manual engagements. The profiling could be
automatically activated driven by the preset conditions."
+tags:
+- eBPF
+- Profiling
+- Tracing
+---
+
+# Background
+
+In previous articles, We have discussed how to use SkyWalking and eBPF for
performance problem detection within
[processes](/blog/2022-07-05-pinpoint-service-mesh-critical-performance-impact-by-using-ebpf)
and [networks](blog/diagnose-service-mesh-network-performance-with-ebpf).
+However, there are still two outstanding issues:
+
+1. **The timing of the task initiation**: It's always challenging to address
the processes that require performance monitoring when problems occur.
+Typically, manual engagement is required to identify processes and the types
of performance analysis necessary, which cause extra time during the crash
recovery.
+The root cause locating and the time of crash recovery conflict with each
other from time to time.
+In the real case, rebooting would be the first choice of recovery, meanwhile,
it destroys the site of crashing.
+2. **Resource consumption of tasks**: The difficulties to determine the
profiling scope. Wider profiling causes more resources than it should.
+We need a method to manage resource consumption and understand which processes
necessitate performance analysis.
+3. **Engineer capabilities**: On-call is usually covered by the whole team,
which have junior and senior engineers, even senior engineers have their
understanding limitation of the complex distributed system,
+it is nearly impossible to understand the whole system by a single one person.
+
+The **Continuous Profiling** is a new created mechanism to resolve the above
issues.
+
+# Mechanism
+
+If profiling tasks consume a significant amount of system resources, can we
find alternative ways to monitor processes that use fewer system resources? The
answer is yes.
+Currently, SkyWalking establishes policy rules for specified target services,
which are then monitored by the eBPF Agent in a low-energy manner.
+When a policy match occurs, a profiling task is automatically triggered.
+
+## Policy
+
+Policy rules specify how to monitor target processes and determine the type of
profiling task to initiate when certain threshold conditions are met.
+
+These policy rules primarily consist of the following configuration
information:
+
+1. **Monitoring type**: This specifies what kind of monitoring should be
implemented on the target process.
+2. **Threshold determination**: This defines how to determine whether the
target process requires the initiation of a profiling task.
+3. **Trigger task**: This specifies what kind of performance analysis task
should be initiated.
+
+### Monitoring type
+
+The type of monitoring is determined by observing the data values of a
specified process to generate corresponding metrics.
+These metric values can then facilitate subsequent threshold judgment
operations.
+In eBPF observation, we believe the following metrics can most directly
reflect the current performance of the program:
+
+| Monitor Type | Unit | Description |
+|--------------|------|-------------|
+| System Load | Load | System load average over a specified period. |
+| Process CPU | Percentage | The CPU usage of the process as a percentage. |
+| Process Thread Count | Count | The number of threads in the process. |
+| HTTP Error Rate | Percentage | The percentage of HTTP requests that result
in error responses (e.g., 4xx or 5xx status codes). |
+| HTTP Avg Response Time | Millisecond | The average response time for HTTP
requests. |
+
+#### Network related monitoring
+
+Monitoring network type metrics is not as simple as obtaining basic process
information.
+It requires the initiation of eBPF programs and attaching them to the target
process for observation.
+This is similar to the principles of [network profiling task we introduced in
the previous
article](blog/diagnose-service-mesh-network-performance-with-ebpf),
+except that we no longer collect the full content of the data packets.
Instead, we only collect the content of messages that match specified HTTP
prefixes.
+
+By using this method, we can significantly reduce the number of times the
kernel sends data to the user space,
+and the user-space program can parse the data content with less system
resource usage. This ultimately helps in conserving system resources.
+
+#### Metrics collector
+
+When the eBPF Agent is monitoring a target process, it would report the
collected data to the SkyWalking backend in the form of metrics.
+This allows users to understand real-time execution status promptly.
+
+| Name | Unit | Description
|
+|------------------------|----------|---------------------------------------------------------------------------|
+| process_cpu | (0-100)% | The CPU usage percent
|
+| process_thread_count | count | The thread count of process
|
+| system_load | count | The average system load for the last
minute, each process have same value |
+| http_error_rate | (0-100)% | The network request error rate
percentage |
+| http_avg_response_time | ms | The network average response duration
|
+
+### Threshold determination
+
+For the threshold determination, the judgement is made by the eBPF Agent based
on the target monitoring process in its own memory,
+rather than relying on calculations performed by the SkyWalking backend.
+The advantage of this approach is that it doesn't have to wait for the results
of complex backend computations,
+and it reduces potential issues brought about by complicated interactions.
+
+By using this method, the eBPF Agent can swiftly initiate tasks immediately
after conditions are met, without any delay.
+
+It includes the following configuration items:
+
+1. **Threshold**: Check if the monitoring value meets the specified
expectations.
+2. **Period**: The time period(seconds) for monitoring data, which can also be
understood as the most recent duration.
+3. **Count**: The number of times(seconds) the threshold is triggered within
the detection period, which can also be understood as the total number of times
the specified threshold rule is triggered in the most recent duration(seconds).
Once the count check is met, the specified Profiling task will be started.
+
+### Trigger task
+
+When the eBPF Agent detects that the threshold determination in the specified
policy meets the rules, it can initiate the corresponding task according to
pre-configured rules.
+For each different target performance task, their task initiation parameters
are different:
+
+* **On/Off CPU Profiling**: It automatically performs performance analysis on
processes that meet the conditions, defaulting to `10` minutes of monitoring.
+* **Network Profiling**: It performs network performance analysis on all
processes in the same **Service Instance on the current machine**,
+to prevent the cause of the issue from being unrealizable due to too few
process being collected, defaulting to `10` minutes of monitoring.
+
+Once the task is initiated, no new profiling tasks would be started for the
current process for a certain period.
+The main reason for this is to prevent frequent task creation due to low
threshold settings, which could affect program execution. The default time
period is `20` minutes.
+
+## Data Flow
+
+The following figure illustrates the data flow of the continuous profiling
feature:
+
+
+
+### eBPF Agent with Process
+
+Firstly, we need to ensure that the eBPF Agent and the process to be monitored
are deployed on the same host machine,
+so that we can collect relevant data from the process. When the eBPF Agent
detects a threshold validation rule that conforms to the policy,
+it immediately triggers the profiling task for the target process, thereby
reducing any intermediate steps and accelerating the ability to pinpoint
performance issues.
+
+#### Sliding window
+
+The sliding window plays a crucial role in the eBPF Agent's threshold
determination process, as illustrated in the following figure:
+
+
+
+Each element in the array represents the data value for a specified second in
time.
+When the sliding window needs to verify whether it is responsible for a rule,
+it fetches the content of each element from a certain number of recent
elements (period parameter).
+If an element exceeds the threshold, it is marked in red and counted. If the
number of red elements exceeds a certain number, it is deemed to trigger a task.
+
+Using a sliding window offers the following two advantages:
+
+1. **Fast retrieval of recent content**: With a sliding window, complex
calculations are unnecessary.
+ You can know the data by simply reading a certain number of recent array
elements.
+2. **Solving data spikes issues**: Validation through count prevents
situations where a data point suddenly spikes and then quickly returns to
normal.
+ Verification with multiple values can reveal whether exceeding the
threshold is frequent or occasional.
+
+### eBPF Agent with SkyWalking Backend
+
+The eBPF Agent communicates periodically with the SkyWalking backend,
involving three most crucial operations:
+
+1. **Policy synchronization**: Through periodic policy synchronization, the
eBPF Agent can keep processes on the local machine updated with the latest
policy rules as much as possible.
+2. **Metrics sending**: For processes that are already being monitored, the
eBPF Agent periodically sends the collected data to the backend program.
+This facilitates real-time query of current data values by users, who can also
compare this data with historical values or thresholds when problems arise.
+3. **Profiling task reporting**: When the eBPF detects that a certain process
has triggered a policy rule, it automatically initiates a performance task,
+collects relevant information from the current process, and reports it to the
SkyWalking backend. This allows users to know **when, why, and what** type of
profiling task was triggered from the interface.
+
+# Demo
+
+Next, let's quickly demonstrate the continuous profiling feature, so you can
understand more specifically what it accomplishes.
+
+## Deploy SkyWalking Showcase
+
+SkyWalking Showcase contains a complete set of example services and can be
monitored using SkyWalking.
+For more information, please check the [official
documentation](https://skywalking.apache.org/docs/skywalking-showcase/next/readme/).
+
+In this demo, we only deploy service, the latest released SkyWalking OAP, and
UI.
+
+```shell
+export SW_OAP_IMAGE=apache/skywalking-oap-server:9.5.0
+export SW_UI_IMAGE=apache/skywalking-ui:9.5.0
+export SW_ROVER_IMAGE=apache/skywalking-rover:0.5.0
+
+export FEATURE_FLAGS=mesh-with-agent,single-node,elasticsearch,rover
+make deploy.kubernetes
+```
+
+After deployment is complete, please run the following script to open
SkyWalking UI: http://localhost:8080/.
+
+```shell
+kubectl port-forward svc/ui 8080:8080 --namespace default
+```
+
+## Create Continuous Profiling Policy
+
+Currently, we can select the specific service that we wish to monitoring by
clicking the **Services** item in the **Service Mesh** panel.
Review Comment:
```suggestion
Currently, continues profiling feature is set by default in the **Service
Mesh** panel at the **Service** level.
```
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