Meeting 22-07-2013

Meeting UoB 22 July 2013

Present: JB, SC, MG, AW, JP, SH, KE, OR

Hardware Energy Monitoring Report (Ashley)

• Slow progress due to needing to get the hardware working
  • Software installation / OS issues
• Moved to use a previous version (V2) energy-monitor boards, since they are more suitable
• Problems using V3 to measure external device energy consumptions
  • Capable but the level of additional soldering required, lack of voltage divider and need for external resistors makes it less easy to use for V2.
• Benchmarks working and verification of their correctness being worked on.
  • TODO: Now a priority to push on internal verification code to the tests.
    • e.g. compare outputs to pre-computed correct and return result.
• When running the benchmarks, we should apply techniques such as externs or volatiles that can store e.g. the final result.
  • Dijkstra program not working, others are.
• TODO: Get the benchmarks (BEEBS / BBS) work for last year out there with more oomph (webs, publicity, workshops...)

• James 13th 14th September will give a talk at OSHCAMP on energy monitoring board design.
• TODO: Run code that straddles flash banks and runs on flash to see differences in energy → feeds well into 'discovery' phase of ML.

MAGEEC Blog posts

• Weekly (ish) blogs, from rotating members of the team.
• TODO: 22/07/2013: Jeremy this week for an intro
• TODO: 29/07/2013: Ashley next week for intro to energy monitoring hardware.
  • Ensure the draft is saved.
  • Andrew will perform the final publishing
• TODO: 05/07/2013: Moon, intro to his work.

Compiler Framework

• No new update on implementation, due to attending GCC meeting etc.
• GCC meeting feedback is that HPC community (inc. LLL) very interested into learning more about low power.
• Looked at the research questions posted from UoB discussion on the wiki.
  • Profile-directed optimisation is very powerful, perhaps most powerful
  • Joern to be quizzed by James about the kinds of profile data that comes out, since it can impact the machine learning.
    • Can some examples of data be generated so that it can be represented for ML learning.

MILEPOST Approach

• Normalised feature vector 0<= 1 using the number of instructions as the divider.
• Ran 1000 random on/off flags, then kept the top 5% of previously trained data.
• Question on whether or not the flags are orthogonal.
• MSc student is addressing:
  • Taking James' flags of significance and isolating these and exhaustively
  • Data set available by end of week.
  • Performance as metric.
• TODO: Paper on James' previous work? Of 130 flags in GCC only 13 make a difference [in our scenarios]. We want to understand why.
• Consider systematic (FFD) vs exhaustive vs random selection and their effectiveness.
  • Part of the MSc work will address this.
• Moon investigating which of the MILEPOST vectors are and are not useful. Needs a large data set of 150+ applications to check them.
  • Work on WCET to extract additional programs to help with this.
  • Look (longer term) at HPC space to augment these.
• MILEPOST Approach Summary: Run with 1000 flags randomly. Having discarded invalid flags, take top 100 good ones and run accumulating stats showing which are in best sets between iterations
• There are techniques for looking at flag dependencies, but they need further investigation.

Framework representation for enabling later advanced ML work

• Reference SC's previous Overall Design slide.

• Oliver outlined the “credit assignment” problem for ML to infer what causes improvement.

• gen_features() just gives a list of passes that will be run.
• Mapping of passes to flags needed.
• A lot of debate about whether to use a feature vector, IR or source code for selecting the relevant features for ML.
• Main takeaway – we need to be able to cope with changes in the features that are relevant as our knowledge of this evolves.
  • Feature info passing should be generic (enough to be able send IR, if necessary).
  • Should plan for plugin re-write next year if necessary to aid this.
• How to support backtracking prediction.
  • Unlikely in GCC due to global state.
• TODO: SC to produce a draft spec by 31/07/2013

Planning

• Hardware design and build completed on time.
• No new streams of work coming online.
• All else proceeding OK.
• TODO: By 29/07/2013: Action the kit buying

Actions carried forward from previous meeting:

• SH: Apply for BlueCrystal Accounts for all
• KIE: To decide on whether for two PCs with 32GB was one PC with two cores and much more RAM