From: Richard <richard_siegfried@systemli.org>
To: kernelnewbies@kernelnewbies.org
Subject: Mutex midpath question (mutex-design.rst , CONFIG_MUTEX_SPIN_ON_OWNER)
Date: Sat, 15 Oct 2022 17:59:36 +0200 [thread overview]
Message-ID: <a9dc09ed-41c2-844b-d14b-7f546d8a9267@systemli.org> (raw)
Hi all,
I have a question regarding understanding mutex-design.rst. It is about
the feature that mutexes also have spinlocks for the case where the
current lock is occupied but by a task that is runnning and might end
soon (optimistic spinning).
The top of the file says:
>
> In its most basic form it also includes a
> wait-queue and a spinlock that serializes access to it. Furthermore,
> CONFIG_MUTEX_SPIN_ON_OWNER=y systems use a spinner MCS lock (->osq), described
> below in (ii).
What is not fully clear for me here is: is the optimistic spinning
always accessible and MCS is just an optimisation. Or is optimistic
spinning only accessible with CONFIG_MUTEX_SPIN_ON_OWNER.
The mentioning of the first spinlock in the first sentence confuses me.
Thanks,
-- Richard
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