linux-kernel - Re: [PATCH v0] add nano semaphore in kernel

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Message-ID: <AANLkTi=0yNQkL3WSP-_GHTEwSb9KuBQmSxC006k-AxDe@mail.gmail.com>
Date:	Wed, 29 Dec 2010 23:03:14 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Daniel Walker <dwalker@...eaurora.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	Mike Christie <michaelc@...wisc.edu>
Subject: Re: [PATCH v0] add nano semaphore in kernel

On Wed, Dec 29, 2010 at 10:58 PM, Daniel Walker <dwalker@...eaurora.org> wrote:
> On Wed, 2010-12-29 at 22:42 +0800, Hillf Danton wrote:
>> On Wed, Dec 29, 2010 at 7:47 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> > On Tuesday 28 December 2010 16:51:30 Daniel Walker wrote:
>> >> We for sure don't want new semaphores, or new semaphore usage in the
>> >> kernel ..
>>
>> Would you please, Daniel, explain why there are so my file systems under
>> the fs directory? Would you think the ext file system is better than others?
>>
>> And why there are in kernel spin lock, read/write lock, mutex, rw_mutex,
>> rtmutx, and semaphore, timer and hrtimer?
>>
>> Could timer be removed tonight?
>
> The problem with semaphores is that people use them in ways that are not
> very nice, and not very efficient.. Since they are so flexible they can
> be used in all sorts of ways, many of which are not clean. This is why,
> if you read the kernel history, most semaphore have been removed from
> the kernel and replaced with much nicer and cleaner mutexes.
>
> Daniel

Thanks for sharing the knowledge about rtmutx and semaphore.
Hillf
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