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Re: Spinlocks, yet again: analysis and proposed patches

Michael Paesold <mpaesold@gmx.at>

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From: "Michael Paesold" <mpaesold@gmx.at>
To: "Marko Kreen" <marko@l-t.ee>, "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: <pgsql-hackers@postgresql.org>
Date: 2005-09-14T20:56:22Z
Lists: pgsql-hackers 
Tom Lane wrote:


>I wrote:
>> We could ameliorate this if there were a way to acquire ownership of the
>> cache line without necessarily winning the spinlock.  I'm imagining
>> that we insert a "dummy" locked instruction just ahead of the xchgb,
>> which touches the spinlock in such a way as to not change its state.
> 
> I tried this, using this tas code:
...

I have tried it on the P4 w/ HT.

CVS tip             1: 37s  2: 78s  4: 159s  8: 324
only slock-no-cmpb  1: 37s  2: 82s  4: 178s  8: 362
only dummy-locking  1: 44s  2: 96s  4: 197s ...

I guess there is no reason to try any more.

Best Regards,
Michael Paesold