linux-kernel - Re: [PATCH 1/2] firmware, fix request_firmware

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Date:	Wed, 23 Oct 2013 21:21:33 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	x86@...nel.org,
	Andreas Herrmann <herrmann.der.user@...glemail.com>,
	tigran@...azian.fsnet.co.uk
Subject: Re: [PATCH 1/2] firmware, fix request_firmware_nowait() freeze with
 no uevent

On Wed, Oct 23, 2013 at 8:02 PM, Prarit Bhargava <prarit@...hat.com> wrote:

>
> After all this I completely forgot the problem I'm trying to solve here.  The
> issue is that with HOTPLUG & request_microcode_nowait(), if the microcode image
> is not found (that is the file is not found on disk), then EACH cpu waits 1
> minute and it takes 2 hours for a 120 cpu box to load the microcode module.
>
> Which is terrible... so HOTPLUG doesn't work here.
>
> Let me back up Ming and see if you have a better solution for me.  I have a
> system that does not have the x86 microcode loaded on disk.  I use the microcode
> module which calls request_firmware_nowait() to load the microcode image and I
> want it done as fast as possible.  The microcode loader does not have a uevent
> so I'm not waiting on userspace for completion.
>
> How do I avoid the 60 second delay/cpu introduced in the microcode path?  I
> don't see one.  If I use HOTPLUG I'm waiting 60 seconds.  If I use NOHOTPLUG
> AFAICT the loading function never will return.  AFAICT the same issue arises
> with the dell_rbu code -- it appears to never load the dell_rbu firmware.

As I said, the 60 second delay is from udev, so that is the root cause.

There are some workarounds for your reference:

- fix udev

- disable CONFIG_FW_LOADER_USER_HELPER if you are sure
the microcode image is under the default firmware search paths, which
are defined in drivers/base/firmware_class.c

- fake a empty latest microcode image under your firmware path

- use request_firmware_nowait(HOTPLUG) to request firmware from
user space, and apply the microcode at a appropriate time after the
request is completed, and the approach is what we are discussing.


Thanks,
--
Ming Lei
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