Activity Monitor %CPU for a task - % of what is indicated?

[Csmac]

I'm puzzled by what the Activity Monitor %CPU indication. I can't find any definitive info relating to what it is being compared to. For instance I have a task running at 36% indicated, but the User CPU at the bottom of the Activity Monitor window is showing 4%. Apple says the CPU indications at the bottom of the window relate to the total possible CPU load, but does not give any info as to what the individual task percentages relate to.

Thanks for any definitive info.

 

[ferrarr]

It will depend on how many processors your Mac has? What Mac are you looking at Activity Monitor on? As an example, if it is a 13" MBP those are usually dual core, while 15" MBP are quad cores. Same for some of the iMac models.

 

[Raz0rEdge]

The values System, User and Idle give you an idea of how much CPU percentage is being used by apps you are running as opposed to the OS. The Idle is, well, percent of your CPU power that is idle. The higher the idle, the more work you can do.

The values on the bottom are an aggregate across the entire system. You can look at each of the running processes above to see how much percentage of the User percentage each process is taking. If you sort by % CPU, you will see a number greater than the aggregate below and that's OK since you are now drilling into what percentage of the aggregate a specific process is taking up.

For example, currently I'm seeing 3.44% System, 7.70% User and the left over in Idle. Google Chrome is taking 8.9% and Microsoft Outlook is taking up 5.9% (or a combined ~16%) of the 7.70% User aggregate.

 

[Csmac]

This is MBP with an i7 processor (see my member info to the left.) i7 has 4 CPU each of which each is dual core so the system says I have 8 CPUs.

My question as stated above is that the task with a large load, 36%, supposedly, is obviously not taking that much load from the system since the total system + User load shown at the bottom is about 8%. So what is it taking 36% of? Totaling all the "active tasks" amounts comes no where close to 100%. Actually I've seen times when 1 task will be showing over 100%. It's not a crucial thing, but it's puzzling. Running Top shows the same percentage as Activity Monitor per task.

 

[pigoo3]

Maybe a visual representation will help. In case you weren't aware...under the "Window" drop down menu in Activity Monitor there's a selection for "CPU Usage". Select it...and a little window will open & you will see a graphical representation of how the CPU cores are being utilized.

Mine looks like this at the moment...it can fluctuate from second to second:



- Nick

 

[pigoo3]

And here's what it looks like just a few moments later (as CPU demand changes with the tasks we do):



- Nick

 

[Csmac]

I am aware of that display. That still doesn't answer the original question of what is the percentage related to. It's not system CPU load for sure. See the attachment for a better indication of what 's I'm asking.

 

[pigoo3]

First look at the % Idle value...in this case 90.55%. This also means 100% - 90.55% = 9.45% used/active CPU resources.

Now consider that the 35.6% for the "Fidigi" process is a percent of a percent. Thus taking the 9.45% total CPU resources used...the 35.6% for "Fidigi" is 35.6% of the 9.45%.

Doing the calculation...9.45% x .356 = 3.3642%.

Thus 3.3642% of TOTAL CPU resources is being used by the "Fidigi" process.

- Nick

 

[Csmac]

Hmmm... You may have it there. I wonder if it might be percent of just the User load since the numbers for Fldigi and the User load change if I display All Processes. Thanks for your time and ideas.

 

[pigoo3]

Hmmm... You may have it there. I wonder if it might be percent of just the User load since the numbers for Fldigi and the User load change if I display All Processes. Thanks for your time and ideas.

Yes...I just looked at things a bit closer. In post #7 (in the image) I see the CPU processes listed are for "My Processes"...I thought it was for "All Processes"...thus my calculations may be off a bit.

The main point in post #8 was...the individual Process Name percentages in the list...are a "percent of a percent"...and this can be converted into an overall single value of how much CPU resources a single process using (per the calculation I made above).

- Nick

 

[MacInWin]

Nick, I don't think that is correct. I have seen the percent well above 100% when driving the CPU hard on my mid-2015, which is impossible if it were a percent of a percent. I think it's the load relative to ONE processor, which makes the math work out as well. So 35.6% of ONE processor, assuming 8 processors, is 4.45% of the TOTAL Power available in all cores. That's close to what the screenshot is showing. Add in the 5.23% of system usage and you have 9.68% total

But I've never seen any authoritative explanation of exactly what Activity Monitor is showing.

 

[Csmac]

MacWin - Good point. I think you've got it. Adding the other percentages shown and dividing by 8 gives 5.4% which is very close to the 5.23% shown for user processes. Assuming the individual percentages shown are rounded then probably it would be even closer if the more accurate numbers were known. That makes a lot of sense to me. Thanks.

 

[pigoo3]

I have seen the percent well above 100% when driving the CPU hard on my mid-2015...

I've also seen percentages above 100%...but as you said...hard to find an authoritative explanation on this. Thus I was hesitant to apply a maximum of 100% to each CPU core or each individual process thread. With a quad-core CPU that would mean a theoretical 400% maximum CPU load...and with supported hyper-threading...that could mean a maximum CPU load of 800%.

I know the app "Handbrake" always uses all available CPU resources. I don't have anything setup at the moment to test Handbrake with...but if someone does...maybe do a quick test with Handbrake. I know all bars in the Activity Monitor Window "CPU Usage" will max-out. Here's a screen shot of what it would look like on a 4 thread computer:



...thus Activity Monitor should display a maximum possible CPU load in CPU process list (All Processes). I've done this before...but I can't remember what my results were.

- Nick