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The problem with a Spinlock...

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  The problem with a Spinlock... aminer <aminer@toto.net> - 2013-09-24 21:36 -0700
    Re: The problem with a Spinlock... aminer <aminer@toto.net> - 2013-09-24 21:46 -0700

#3796 — The problem with a Spinlock...

Hello,

That's not the end of the story, there is still a problem
with the Spinlock with an exponential backoff, i think you have
to undertand something important, the backoff mechanism has
to be set correctly to lower the cache-coherence traffic,
but how to set it correctly ? cause the locked region has
a variable size , so if for example your locked region
takes much more time and it's bigger you have to set the
backoff mechanism with the PAUSE asm instruction(followed by a
sleep(0)) correctly so that it will be bigger than  what it
takes to execute the locked region , so this is the problem with
the Spinlocks with backoff , so how can we you do that efficiently?
that's the big question ! and i think it's not easy to do it, for
the lockfree queues, the time to execute a CAS is already known,
so you can set the backoff mechanism of the lockfree queue correctly
so that it become efficient under high contention.



Thank you,
Amine Moulay Ramdane.

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#3797

I correct a typo, please read again:

Hello,

That's not the end of the story, there is still a problem
with the Spinlock with an exponential backoff, i think you have
to undertand something important, the backoff mechanism has
to be set correctly to lower the cache-coherence traffic,
but how to set it correctly ? cause the locked region has
a variable size , so if for example your locked region
takes much more time and it's bigger you have to set the
backoff mechanism with the PAUSE asm instruction(followed by a
sleep(0)) correctly so that it will be bigger than  what it
takes to execute the locked region , so this is the problem with
the Spinlocks with backoff , so how can we you do that efficiently?
that's the big question ! and i think it's not easy to do it, but for
the lockfree queues, the time to execute a CAS is already known,
so you can set the backoff mechanism of the lockfree queue correctly
so that it become efficient under high contention.



Thank you,
Amine Moulay Ramdane.

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