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SubjectRe: [PATCH 1/2] firmware, fix request_firmware_nowait() freeze with no uevent
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On Wed, Oct 23, 2013 at 8:02 PM, Prarit Bhargava <prarit@redhat.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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