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<== Date ==> <== Thread ==>

Subject: Re: "spinlock" API
From: Michael Davidsaver <mdavidsaver@bnl.gov>
To: core-talk@aps.anl.gov
Date: Tue, 12 Jun 2012 10:13:31 -0400
On 6/11/2012 6:31 PM, Michael Davidsaver wrote:
On 6/11/2012 5:16 PM, Andrew Johnson wrote:
...
Can we design the default implementation to use atomic variables instead of
mutexes, unless there really is no alternative?

To be honest, I'm a little unsure what the performance implications of a spinlock implementation would be when task preemption can't be disabled.

Just to be clear, I'm thinking of starvation issues like priority inversion which can arise when the OS scheduler does not "know" about the locking.


On a workstation OS the act
of taking or releasing a mutex always requires a context switch, whereas an
atomic operation does not.

Is this true? I thought that a syscall was required, but that the full context switch only occurs if the lock is contested.

http://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_mutex_lock.c#l44

It seems that glibc can actually avoid a syscall in some cases. This is implemented with an atomic test operation.

http://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/lowlevellock.h


Michael


Replies:
Re: "spinlock" API Andrew Johnson
References:
"spinlock" API Michael Davidsaver
Re: "spinlock" API Andrew Johnson
Re: "spinlock" API Michael Davidsaver
Re: "spinlock" API Andrew Johnson
Re: "spinlock" API Michael Davidsaver

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