linux-kernel - Do not deprecate binary semaphore or do allow mutex in software interrupt contexts

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Message-ID: <432622.65445.qm@web52004.mail.re2.yahoo.com>
Date:	Tue, 11 Sep 2007 10:29:19 -0700 (PDT)
From:	Matti Linnanvuori <mattilinnanvuori@...oo.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	arjan <arjan@...radead.org>
Subject: Do not deprecate binary semaphore or do allow mutex in software interrupt contexts

Peter Zijlstra <peterz@...radead.org>:
> Yes it is.

Why do you think it is broken?

> If you have to wait a long time in an atomic context you've done
> something wrong.

I saw an implementation where there were two atomic contexts, one to initiate reading and another to complete the reading. 
That way, there was no busy wait for a long time in an atomic context.

> If you're only reading it from an atomic context you
> might consider storing a copy that can be quickly updated and protect
> that using a spinlock.

You suggested that a user-space task read from the device. 
But that includes more context switching and therefore consumes more resources than reading just from an atomic context.

> Not being too familiar with the timer stuff, it smells wrong what you
> say.

Why?




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