Ubuntu

High hardware interrupts cpu % usage

Asked by Charles Perreault

I'm using Dapper with kernel 2.6.15-26 on a Compaq V2000z laptop, 2 gb ram, Turion MT-40. Sometimes, when the computer is idle, the hardware interrupt cpu usage jumps to near 100% and even scales my cpu frequency to full speed, which I truly hate when running in battery mode. "top" reports an average of 20-40% of hi (hardware interrupts) using the cpu, and it rarely goes under 20%.

Something must be wrong to have such a high cpu usage % in hardware interrupts. I don't recall when this behaviour started, but it is observed also on -25 kernel. Is there a way to diagnose what is causing all those interrupts ?

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Roberto Rosario (roberto-rosario-gonzalez) said : 		#1

execute "watch -d cat /proc/interrupts " on a terminal windows and see which one increases faster. Also what size is your swap partition (should be 1.5 to 2 x RAM), the kernel may be trying to page out stale RAM content to an unavailable swap space.

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Best Charles Perreault (muganor) said : 		#2

I don't have a swap space, I don't believe I need one; my memory usage is usually far less than the capacity. My memory space is 2 GB which is more than people using 512mb + 1gb swap space. Swaping makes use of HDD which is very slow on a laptop.

I'm now using kernel 2.6.15-27 and the problem has disappeared in the last month, but I don't know why. I changed the HDD because the previous one had several bad sectors and failed SMART checks. I recall the hard drive was under heavy use during the high cpu usage I described above, it may be related. If I meet the problem again, I will try watching /proc/interrupts as you ask and add a swap space to check for change, but for now the support request can be closed. Thank you very much.