Re: [Xen-devel] [PATCH v7 09/10] microcode: remove microcode_update_lock

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.06.19 at 16:52, <roger.pau@xxxxxxxxxx> wrote:
> On Mon, May 27, 2019 at 04:31:30PM +0800, Chao Gao wrote:
>> microcode_update_lock is to prevent logic threads of a same core from
>> updating microcode at the same time. But due to using a global lock, it
>> also prevented parallel microcode updating on different cores.
> 
> Oh, OK, so that's what I was missing from patch 8 and what serializes
> the updating.
> 
>> Remove this lock in order to update microcode in parallel. It is safe
>> because we have already ensured serialization of sibling threads at the
>> caller side.
> 
> Then you certainly need to fix the wait loop in do_microcode_update to
> only wait for MICROCODE_UPDATE_TIMEOUT_US regardless of the number of
> CPUs in the system?

Well, no, not exactly. On huge systems it may indeed still take longer
than on smaller ones. The way the waiting is coded now (expecting
forward progress in every MICROCODE_UPDATE_TIMEOUT_US period, is,
I think, acceptable. Plus leaving that logic alone will avoid touching it
yet again when introducing serial application policy as an option.

Jan



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