Messages in this thread | | | Date | Mon, 19 Apr 2010 09:11:54 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 1/5] Add a global synchronization point for pvclock |
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On 04/19/2010 07:33 AM, Avi Kivity wrote: > On 04/19/2010 05:21 PM, Glauber Costa wrote: >> >>> Oh yes, just trying to avoid a patch with both atomic64_read() and >>> ACCESS_ONCE(). >>> >> you're mixing the private version of the patch you saw with this one. >> there isn't any atomic reads in here. I'll use a barrier then >> > > This patch writes last_value atomically, but reads it non-atomically. > A barrier is insufficient.
Well, on a 32b system, you can explicitly order the updates of low and high, then do a high-low-checkhigh read. That would be much more efficient than atomic64. If we really care about 32b.
J
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