Subject: Re: [PATCH v0] add nano semaphore in kernel
From: Daniel Walker <dwalker@codeaurora.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Hillf Danton <dhillf@gmail.com>, linux-kernel@vger.kernel.org
In-Reply-To: <201012272215.52642.arnd@arndb.de>
References: <AANLkTim0Xmsnzz5yMLAx_+w-c7sSSReu0SKMAmjpbS+1@mail.gmail.com>
	 <201012272215.52642.arnd@arndb.de>
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Date: Tue, 28 Dec 2010 07:51:30 -0800
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On Mon, 2010-12-27 at 22:15 +0100, Arnd Bergmann wrote:
> On Sunday 26 December 2010, Hillf Danton wrote:
> > 
> > Based upon high resolution timer and idea borrowed from semaphore,
> > nano semaphore is created.
> > 
> > Nano semaphore provides finer time resolution depending on system
> > configuration and capabilities.
> > 
> > Nano semaphore is not to replace semaphore, but used in application
> > environments where nano seconds are required.
> > 
> > Three methods, nano_semaphore_try_down, nano_semaphore_down and
> > nano_semaphore_up are implemented in a header file, and there is no
> > corresponding C file since nano semaphore is not complex.
> > 
> > Signed-off-by: Hillf Danton <dhillf@gmail.com>
> 
> There are very few users of real semaphores today, and we're trying to
> get rid of them. It's not clear what your requirements are, since you
> have not posted any new users of this, but instead of adding more
> locking primitives, I would recommend changing one of the existing
> ones (mutex, semaphore, rwsem) to have nanosecond timeouts instead
> of jiffies.
> 
> The easiest way would certainly be to change the three users of
> down_timeout() to use nanoseconds.

We for sure don't want new semaphores, or new semaphore usage in the
kernel ..

It should also be noted that the rtmutex (kernel/rtmutex.c) already has
this capability. Although I don't think you can use an rtmutex from
inside the kernel.

If you really want this you should look into the rtmutex, and the
regular mutex API's .

Daniel


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