linux-kernel - Re: Profiling execution time for __alloc_pages

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Message-ID: <CAHbLzko8rHfE-3k=e+fdW2+S1Cc0his8-=Ch08HuMMmf=RJsDg@mail.gmail.com>
Date:   Mon, 10 May 2021 17:00:22 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Shivank Garg <shivankgarg98@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        gregkh@...uxfoundation.org, sergey.senozhatsky@...il.com,
        pmladek@...e.com, David Hildenbrand <david@...hat.com>
Subject: Re: Profiling execution time for __alloc_pages_nodemask

On Mon, May 10, 2021 at 7:57 AM Shivank Garg <shivankgarg98@...il.com> 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.
> 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)

Is there any reason that prevents you from using some advanced tools,
i.e. perf, bcc/bpftrace, etc? They are much simpler than adding
instrumentation in kernel.

>
> 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)
>
> Stay Safe!
> Best Regards,
> Shivank Garg
> Open-Source Enthusiast and Student, IIT Kanpur
>