linux-kernel - Re: [PATCH v3] kernel/module: Reschedule while waiting for modules to finish loading

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Message-ID: <20190502094813.GA6690@linux-8ccs>
Date:   Thu, 2 May 2019 11:48:14 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        David Arcari <darcari@...hat.com>
Subject: Re: [PATCH v3] kernel/module: Reschedule while waiting for modules
 to finish loading

+++ Prarit Bhargava [01/05/19 17:26 -0400]:
>
>
>On 4/30/19 6:22 PM, Prarit Bhargava wrote:
>> On a s390 z14 LAR with 2 cpus about stalls about 3% of the time while
>> loading the s390_trng.ko module.
>>
>> Add a reschedule point to the loop that waits for modules to complete
>> loading.
>>
>> v3: cleanup Fixes line.
>
>Jessica, even with this additional patch there appears to be some other issues
>in the module code that are causing significant delays in boot up on large
>systems.

Is this limited to only s390? Or are you seeing this on other arches
as well? And is it limited to specific modules (like s390_trng)?

>Please revert these fixes from linux-next & modules-next.  I apologize for the
>extra work but I think it is for the best until I come up with a more complete &
>better tested patch.

Sure, then I will revert this patch and the other one as well
("modules: Only return -EEXIST for modules that have finished
loading").

>FWIW, the logic in the original patch is correct.  It's just that there's, as
>Heiko discovered, some poor scheduling, etc., that is impacting the module
>loading code after these changes.

I am really curious to see what these performance regressions look
like :/ Please update us when you find out more.

>Again, my apologies,

No problem! Thanks again.

Jessica