linux-kernel - Re: [PATCH v2 00/14] Introducing TIF_NOTIFY

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Message-ID: <4f872eec-f302-5ac4-e914-bcc3ce65950c@amd.com>
Date: Mon, 17 Jun 2024 10:05:36 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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Subject: Re: [PATCH v2 00/14] Introducing TIF_NOTIFY_IPI flag

Hello Russell,

On 6/15/2024 7:56 PM, Russell King (Oracle) wrote:
> On Thu, Jun 13, 2024 at 06:15:59PM +0000, K Prateek Nayak wrote:
>> o Dropping the ARM results since I never got my hands on the ARM64
>>    system I used in my last testing. If I do manage to get my hands on it
>>    again, I'll rerun the experiments and share the results on the thread.
>>    To test the case where TIF_NOTIFY_IPI is not enabled for a particular
>>    architecture, I applied the series only until Patch 3 and tested the
>>    same on my x86 machine with a WARN_ON_ONCE() in do_idle() to check if
>>    tif_notify_ipi() ever return true and then repeated the same with
>>    Patch 4 applied.
> 
> Confused. ARM (32-bit) or ARM64? You patch 32-bit ARM, but you don't
> touch 64-bit Arm. "ARM" on its own in the context above to me suggests
> 32-bit, since you refer to ARM64 later.
> 

In my first RFC posting, I had shared the results for ipistorm on an
ARM64 server [1]. Vincent and Linus Walleij brought to my attention that
ARM32 and ARM64 do not share the thread info flags and I probably saw a
one-off behavior during my testing. Since then, it has been slightly
challenging to get my hands on that machine again in a stable condition
to see if there was any scenario that I might have missed but I tried a
bunch of things on my x86 machine to confirm that an arch that does not
define the TIF_NOTIFY_IPI would not hit these changes.

Rest assured, Patch 5 is for ARM32 machines that currently define
TIF_POLLING_NRFLAG

[1] https://lore.kernel.org/lkml/20240220171457.703-6-kprateek.nayak@amd.com/

-- 
Thanks and Regards,
Prateek