Re: Profiling execution time for __alloc_pages_nodemask

[David Hildenbrand]

On 10.05.21 16:57, Shivank Garg wrote:
> Hi Everyone!
>
> I want to profile the time taken to execute the __alloc_pages_nodemask
> for different linux configurations/parameters.
> To measure the execution time, I use the ktime_get() apis. I get the
> ktime_get() on the top, and I want to do ktime_sub(ktime_get(),ktime)
> and record it in a tracepoint.

Don't tracepoints already record a timestamp? It's bee a while since I 
worked with tracepoints ...

> However, the patch on implementation prevents the kernel from booting
> up. I debugged the bug to find out that the issue recurs on adding
> ktime_get() inside the __alloc_pages_nodemask path. So, that the
> kernel fails to boot up ( and show the blank screen without any logs )
> I'm using the Linux kernel 5.6.13 (5821a5593fa9f28eb6fcc95c35d00454d9bb8624)

Are you maybe calling ktime_get() too early during boot, where some 
subsystems are just about to be brought up?

> Is it an expected behavior? or a BUG? Has anyone else faced the same issue?
>
> Can you please suggest, what would be a good way to measure execution
> time for page allocation (if not ktime_get)

I could have sworn ordinary tracepoints would already give you a 
timestamp ...

--
Thanks,

David / dhildenb