linux-kernel - Re: [PATCH] profiling: remove prof_cpu

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Message-ID: <87a5i2ttv0.ffs@tglx>
Date: Sat, 27 Jul 2024 23:20:19 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>, Tetsuo Handa
 <penguin-kernel@...ove.sakura.ne.jp>
Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>, Andrew Morton
 <akpm@...ux-foundation.org>, Arnd Bergmann <arnd@...db.de>, Mel Gorman
 <mgorman@...hsingularity.net>, Michal Hocko <mhocko@...e.com>, Peter
 Zijlstra <peterz@...radead.org>, Vlastimil Babka <vbabka@...e.cz>, Ingo
 Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] profiling: remove prof_cpu_mask

On Sat, Jul 27 2024 at 09:54, Linus Torvalds wrote:
> On Sat, 27 Jul 2024 at 04:00, Tetsuo Handa
> <penguin-kernel@...ove.sakura.ne.jp> wrote:
>>
>> We could replace alloc_cpumask_var() with zalloc_cpumask_var() and
>> call cpumask_copy() from create_proc_profile() on only UP kernels, for
>> profile_online_cpu() calls cpumask_set_cpu() as needed via
>> cpuhp_setup_state(CPUHP_AP_ONLINE_DYN) on SMP kernels. But this patch
>> removes prof_cpu_mask because it seems unnecessary.
>
> So I like this one a lot more, but it actually makes me wonder: could
> we just remove the horrid per-cpu profile flip buffers entirely?
>
> This code predates the whole "we have _real_ profiling", and dates
> back to literally two decades ago.
>
> It's there due to ancient NUMA concerns on old SGI Altix hardware in 2004:
>
>    https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=ad02973d42f6b538c7ed76c7c0a5ae8560f65913
>
> and I think it's past time to just take all this code out of its misery.
>
> Nobody sane should use the old profile code for any real work any
> more. I'd be more than happy to just remove all the magic code and see
> if anybody even notices..

Only people who indulge in nostalgia will notice :)