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Light Wellness 101

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Logan Adams
Logan Adams


This article helps you identify the cause of sustained high CPU usage. Keep in mind that you can expect CPU usage to increase as a process or an application serves requests. However, if you consistently see CPU usage remain at a high level (80 percent or greater) for prolonged periods, the performance of your system or application will suffer. For that reason, it's important to understand the cause of sustained high CPU usage to be able to correct the problem, if possible.


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Select the Average CPU column header to sort the list by overall CPU usage. Make sure that the arrow that appears on the header points down to sort the data from highest to lowest CPU consumption.

If a svchost process consumes high CPU usage, and the svchost process contains more than one service, you need to break each service out to run in its own svchost process to determine which service is causing the high CPU usage. To do so, follow these steps:

Dropbox uses several processes to store, sync and update your files. Dropbox also checks for version updates and performs self-monitoring tasks. These tasks can increase CPU usage and may slow down your computer.

Assume that you query a binary large object (BLOB) column in Microsoft SQL Server 2008 R2 or in Microsoft SQL Server 2012 on a computer that has multiple CPUs. The query uses the NOLOCKhint. In this situation, you experience high CPU usage on the computer.Note This issue is more likely to occur if the computer has 16 or more CPUs installed.

That about sums it up! Let us know if you have any other niche fixes for high CPU usage; as always, comment down below and, if you feel like it, join our forum to discuss all things PC!

In this guide, we are going to explore why this happens, and why W3WP high CPU usage can negatively impact and even take down IIS websites (due to hangs, thread pool exhaustion, queueing/503 queue full errors, and more).

Instead, the top causes of w3wp exe high CPU usage tend to be application code aspects that you would normally never think about or see during testing, but nonetheless happen when the application experiences peak traffic or an unexpected workload. Things like:

This partially explains why code reviews, and even proactive testing/tuning in a test environment, often fails to find the true cause of production CPU overloads. Without knowing exactly what code is causing the high w3wp CPU in production at the EXACT TIME of the overload, you are probably optimizing the wrong code!

Instead, all we need to do is determine the application code causing the high CPU usage in the IIS worker process, at the exact time when it causes a hang or website performance degradation in production.

The knee jerk reaction is to throw more hardware at the problem, which then also ensures that the hosting costs/cloud costs for running your application are 2-5x higher than they really need to be. At the same time, the application likely still experiences high CPU usage and overloads during peak traffic.

High worker process CPU usage often causes severe performance degradation because of the complex interplay between the async/parallel nature of modern web application code, thread pool starvation and exhaustion, and garbage collection. We explain these regressive mechanisms in detail below.

Your IIS monitoring strategy for CPU overloads needs to include monitoring IIS website performance together with CPU usage. The CPU overload exists when the CPU usage of the worker process or server is high, AND performance is degraded.

If your workload is elastic wrt. CPU usage, you may see a very small change in slow requests, even if all your requests are slightly slower. In this case, congratulations, you are making great use of your server processing bandwidth!

When the CPU usage on the server exceeds 81%, the thread pool stops creating new threads, even if the number of threads is well below the configured maximum limit. When combined with blocking operations, even if they are short lived, this can rapidly cause the thread pool to run out of threads. As a result, new requests being pumped into the worker process will queue up waiting for CLR threads.

Most modern ASP.NET applications heavily rely on asynchronous tasks, and some use parallel tasks to take better advantage of multi-core processing power (the latter usually turns out to be a BAD idea in already highly concurrent web applications). Async is normally great for reducing thread pressure in the system, and scaling to high workload concurrency without hitting thread pool exhaustion.

Under high CPU usage, this competition can create an effective deadlock, where existing requests are unable to complete because the available threads are being occupied by new requests coming into the system. This can be particularly bad because async applications usually get by with very few threads, so when the high CPU usage hits, the system may be unable to scale the thread pool to the completion demands of the async workload.

If you have LeanSentry, it will automatically diagnose 503 Queue Full incidents as I mentioned earlier, but also proactively look at your IIS thread usage and identify potential blockages that can lead to queue full issues earlier than normal:

When w3wp has high CPU usage, and you are experiencing thread delays due to thread pool starvation, task starvation, and just generally slower code execution, you are much more likely to experience timeouts in the application code.

We covered the main reasons why high CPU usage can cause poor website performance, even when the server processor is not completely overloaded. In my opinion, fixing these is MUCH more valuable than tuning the application code to have lower CPU usage, because it makes your application more resilient and scalable at higher load.

In cases where the server CPU is completely overloaded, the ETW profiling approach may fail to generate good results. This happens because ETW is fundamentally designed to be a lossy system to maintain low tracing overhead. As such, ETW automatically drops events if the system is overloaded. If the trace loss is high enough, an ETW profiler will not be able to properly construct stack traces needed to tie the CPU usage down to code.

The idea is simple: if the IIS worker process is using so much CPU that the server is completely overloaded, you are able to clearly identify the functions causing the CPU usage simply by viewing a point-in-time snapshot of the executing code.

If you are using LeanSentry, the CPU diagnostic report makes this analysis simple for you, by showing you a merged tree of the application code by its CPU usage. You can drill into the tree to visually navigate the code pathways contributing the most CPU usage:

As a developer, I personally love the bottom up cases, because they give me an opportunity to fire up Linqpad and test out some creative code optimization ideas. For example, if you are using JSON serialization to store some data, and that causes high CPU overhead, you can test out a more efficient serialization scheme like protobuf-net by Marc Gravell.

If you are having high CPU issues, and are looking for a fast way to resolve them correctly, check out LeanSentry CPU diagnostics. This can dramatically simplify the process of catching and diagnosing CPU usage problems for your website, without the traditional overhead associated with profiling in production.

My final recommendation is to first focus on making your application elastic, so that it does not hang/stutter under high CPU usage. Then, use the CPU diagnostics to incrementally optimize it to increase website performance and lower hosting costs.

This approach is key to preventing future performance issues when the CPU goes high, so your optimization efforts can be about yielding proactive improvements as opposed to high stress reactions to severe production incidents.

I was facing this problem a lot.My CPU usage would reach above 1000 percent and most of it would be by Kernel_task. Whenever we connect second display or use heavy applications ,it requires more gpu/cpu power so our computer heats up more. If the temperature rises too high, Mac Os will run a dummy process "Kernel_task" to reserve cpu usage but keep it idle to reduce load of cpu and protect the computer from burning. As the temperature lowers it will release the resources. The problem in my case was accumulation of dust in the CPU and GPU fan.It had probably sucked it through the side vents. I cleaned it and it works like breeze. I even changed the thermal paste on my CPU and GPU as it had become hard over time and excessive heating. Hope this helps.

@joeltom21, yes you need to open up your case. But, if you are in US, you can make a Genius Bar appointment at apple store and ask them to open you laptop and clean the fans. They don't charge for this and very safe way to do it as they have appropriate pentalobe screwdriver etc. I had exact same issue with with my MBP, where connecting external monitors would make a 2019 model useless duet o kernel_task cpu usage. When I got the fans cleaned at Apple store, my MacBook was back in game. I am now able to connect two monitors with no issues whatsoever. My MBP runs without any noise where as earlier it used to due to the dust trapped in fans reducing their cooling efficiency.

I was having this problem recently also. Depending on what year your Macbook Pro is... if you have the power (charging) cable plugged into the left side. I would recommend first trying to move the power to the right side of your laptop. This is apparently a known issue with 2019 MBP's especially with the 16 inch model. Also, I found that because i had purchased a magnetic adapter online for my power cable, when i removed it, the high kenel task magically disappeared. Id recommend trying the same!

Same issue with my 2016 Macbook Pro 15". It was a dual monitor setup, one being a super ultra wide and one regular. No issues whatsoever until all of the sudden it was slower than molasses. Turns out my MacBook was extremely hot (In clamshell mode) even though I'm running fans at full blasts and CPU only reads 50-62 degrees Celsius. Opened the laptop for about minute and it cooled down immediately and kernal usage dropped like a brick on the CPU. My system CPU usage went from 85% to 5% after the laptop cooled down while being open. I read one response on here regarding the charging thunderbolt cable being on the left side, so I've switched to the right to check on how it would handle clamshell mode now. For now it seems fine, though I'm sure that may change here in a couple hours. Respond here and I'll try to report back with an update. 041b061a72


Light wellness is not a fad, nor a hoax. Light cannot change...


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