Merge pull request #1080 from apradhana/TSC_2021-05-25

Add TSC Meeting Notes from 2021-05-25.

Author: apradhana

tsc/meetings/2021-05-25.md

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+Minutes from 92nd OpenVDB TSC meeting, May 25th, 2021, (EDT)
+
+Attendees: *Nick* A., *Ken* M., *Jeff* L., *Dan* B., *Andre* P.
+
+Additional Attendees: Richard Jones (DNeg), JT Nelson (Blender), 
+Bruce Cherniak (Intel), Sergio Rojas, Johannes Meng (Intel).
+Jeff Budsberg (DreamWorks)
+
+
+Regrets: None
+
+Agenda:
+
+1) Confirm Quorum
+2) Secretary
+3) TSC Updates
+4) OpenVDB 8.1
+5) Siggraph Course
+6) Vectorization
+7) Intel's OpenCL and TBB 2021
+8) Support for LLVM 6 in AX
+9) Github Pages
+10) PR-1050 (Blind Data)
+11) PR-1024 (DynamicNodeManager Grain Size)
+12) PR-1070
+13) Next meeting
+
+1) Confirm Quorum
+
+Quorum is present.
+
+2) Secretary
+
+Secretary is Andre Pradhana.
+
+3) TSC Updates
+
+Nick is changing employers. This is going to happen at the end of June 2021.
+He intends to still be part of the TSC. Nick nominates Richard Jones to be a member
+of the TSC. Ken mentions that members of the TSC need to be active developers and
+that it is of interest to have somebody from DNEG as part of ASWF. Dan vouches that
+Richard is a good and competent developer and it will be good to have him
+as a member of the TSC.
+
+
+4) OpenVDB 8.1
+
+We have one more week before the release of OpenVDB 8.1. Dan mentions that there is not
+going to be too much testing from ILM because the major release is done on a quarterly
+basis. Jeff was waiting for a branch for the 8.1 version. Dan will create a branch for 8.1
+today. Andre has a test map for OpenVDB 8.1 in DWA, he is working with Ibrahim on
+the in-house build system. 
+
+5) Siggraph Course
+
+Ken will not change Nick's affiliation for the course.
+
+The deadline of getting the recording to JT is this Friday, May 28, 2021. Everybody
+will email a video to JT. However if you need more time, JT will accommodate until
+Wednesday June 2nd, 2021.
+
+Jeff mentions that he did a zoom-recording test-run with screen-sharing for Houdini
+session versus presentation. He discovers that screen sharing puts his icon besides
+the window. JT believes that you can change this setting and he is going to look into it.
+Ken may need more time because he may need to serve in a jury duty, but he will finish
+the course by the weekend at the latest.
+
+Everyone is fine with the order of the course. 
+
+Nick brings up comparison between AX and OpenVDB C++ API. Dan does not have any plans
+on vectorization. He wants to talk about how to write parallel-algorithm with VDB.
+For the course, Nick and Richard want to bring up the point that AX will be able
+to exploit the underlying host's architecture for optimization. To highlight this
+they want to compare AX with existing parallel method in OpenVDB such as the
+LeafManager's foreach and tools::foreach. Richard has examples for setting the values
+and decrement the values by 1. Dan and Ken mentions that tools::foreach is using the
+nested iterator and is expected to be slower than the LeafManager's foreach. Later,
+Nick mentions that tools::foreach is the easiest way to execute across all levels
+of a VDB tree.
+
+Ken mentions that somebody in the course should talk about the road map for OpenVDB.
+He will get an email rolling.
+
+6) Vectorization
+
+Ken wants to push for vectorization (e.g. AVX) in OpenVDB. There are many places where
+we can benefit by using vectorization in the tools. Ken and Nick mentions the need to use
+a wrapper library to implement vectorization correctly. There is pitfall if you blindly
+puts AVX everywhere because there are cases where you slow it down because populating
+the SSE registers can be expensive. Jeff mentions the issue with downclocking with
+AVX-512 and processor compatibility.
+
+Nick uses Agner's Fog VCL vectorization library. Dan mentions that since we already have
+a way to introduce half into the library, we also needs to consider embedding the library
+into OpenVDB especially because it is header only. Nick says that there are two versions
+of the library for C++14 and C++17. The former version is completely locked. 
+
+Jeff mentions processor compatibility issues that may rise up. There is also a problem
+with getting two different results of fused multiply-add from a code compiled with and
+without AVX2. Dan also had an experience of getting different results from a GPU code
+and a code running on the CPU, where he needed to turn off fused multiply-add on the CPU
+to get the same results.
+
+Nick mentions that Windows does not have flags for anything before AVX that makes it
+impossible to detect the host architecture at compile time through MS build.
+
+
+7) Intel's OpenCL and TBB 2021
+
+Dan asks if anyone from Intel (Bruce or Johannes) has a direct contact with the OpenCL
+team because the new OpenCL driver with the latest tbb does not work in CentOS 7. Johannes
+suggests Dan to send an email to him and Bruce.
+
+Johannes and Nick talk about the tbb 2021 fix. Some fixes will get into 8.1, but not
+it is still incomplete and Nick asks for people to contribute. It is not a priority for
+8.1.
+
+8) Support for LLVM 6 in AX
+
+Nick wants to drop support for LLVM 6 in AX. Nick asks Dan if he can change
+OPENVDB_FUTURE_DEPRECATION to be ON. Dan has no objection.
+
+9) Github Pages
+
+Nick asks for what lives in the OpenVDB repository, including the website and
+documentation. Dan says that the documentation is part of the code. Dan thinks
+that ideally the documentation should live on the OpenVDB website repo. Nick
+wants to take a look at an ideal solution for this. Nick has been playing
+around with getting Read the Docs to work with OpenVDB.
+
+10) PR-1071 (Code Coverage)
+
+Nick has a code coverage pull request based on gcov. The Fast Sweeping test in
+debug build takes very long to complete. Ken will take a look into this. Nick
+says that the Levelset Filter is not tested. Nick also is experimenting with
+clang instead of gcov.
+
+Dan sees that this test coverage only covers one ABI. It will be nice to have
+a coverage test more frequently, even with every PR. It is very cool to have this
+coverage test.
+
+10) PR-1050 (Blind Data)
+
+Dan thinks that this PR is ready to go. This is ABI 9 feature. Ken will look
+at this PR.
+
+11) PR-1024 (DynamicNodeManager Grain Size)
+
+There is grain size for leaf nodes and another for non-leaf nodes. Jeff wants a good
+way to know the size of the tree and decide on whether an algorithm should be threaded
+based on that. This is related to having 8 root nodes problem.
+
+In the end, Jeff and Ken have no objections. Ken mentions that we should revisit the
+positioning of the origin, but we should start with some benchmarks.
+
+12) PR-1070
+
+The CI is currently broken, since brew has updated to tbb 2020. This PR fixes it.
+
+13) Next meeting
+
+Next meeting is June 1st, 2021. 12pm-1pm EST (GMT-5).
+