Re: [linux-next:master] [cpuidle] 38f83090f5: fsmark.app_overhead 51.9% regression

[Christian Loehle <christian.loehle@arm.com>]

On 10/7/24 16:18, Rafael J. Wysocki wrote:
> On Mon, Oct 7, 2024 at 4:44 PM kernel test robot <oliver.sang@intel.com> wrote:
>>
>>
>>
>> Hello,
>>
>> kernel test robot noticed a 51.9% regression of fsmark.app_overhead on:
> 
> What exactly is fsmark.app_overhead?  What does it measure?

"App overhead is time in microseconds spent in the test not doing file writing related system calls."
So the loop is:
	/*
	 * MAIN FILE WRITE LOOP:
	 * This loop measures the specific steps in creating files:
	 *      Step 1: Make up a file name
	 *      Step 2: Creat(file_name);
	 *      Step 3: write file data
	 *      Step 4: fsync() file data (optional)
	 *      Step 5: close() file descriptor
	 */

And it gets the timestamps before and after each syscall.
It then subtracts all those times (spent in syscalls) from the total time.
I'll go take a look tomorrow, what's interesting is that the exit-latency
(which is the thing supposed to cause regressions here) should be time
spent blocking on syscalls.
If that is all correct that's the part that shouldn't regress on cpuidle.