On 2017/2/14 3:06, Paul E. McKenney wrote:
On Mon, Feb 13, 2017 at 09:55:50PM +0800, Yubin Ruan wrote:
It have been mentioned in the book that there are three kinds of
memory barriers: smp_rmb, smp_wmb, smp_mb
I am confused about their actual semantic:
The book says that(B.5 paragraph 2, perfbook2017.01.02a):
for smp_rmb():
"The effect of this is that a read memory barrier orders
only loads on the CPU that executes it, so that all loads
preceding the read memory barrier will appear to have
completed before any load following the read memory
barrier"
for smp_wmb():
"so that all stores preceding the write memory barrier will
appear to have completed before any store following the
write memory barrier"
I wonder, is there any primitive "X" which can guarantees:
"that all 'loads' preceding the X will appear to have completed
before any *store* following the X "
and similarly:
"that all 'store' preceding the X will appear to have completed
before any *load* following the X "
I am reading your the material you provided.
So, there is no short answer(yes/no) to the questions above?(I mean the
primitive X)
I know I can use the general smp_mb() for that, but that is a little
too general.
Do I miss/mix anything ?
Well, the memory-ordering material is a bit dated. There is some work
underway to come up with a better model, and I presented on it a couple
weeks ago:
http://www.rdrop.com/users/paulmck/scalability/paper/LinuxMM.2017.01.19a.LCA.pdf
This presentation calls out a tarball that includes some .html files
that have much better explanations, and this wording will hopefully
be reflected in an upcoming version of the book. Here is a direct
URL for the tarball:
http://www.rdrop.com/users/paulmck/scalability/paper/LCA-LinuxMemoryModel.2017.01.15a.tgz
Thanx, Paul
regrads,
Yubin Ruan
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