decrease event size by storing PFCandidates with half precision float… #29513
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Code check has found code style and quality issues which could be resolved by applying following patch(s)
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A new Pull Request was created by @jsalfeld (Jakob Salfeld-Nebgen) for master. It involves the following packages: HLTrigger/JetMET @cmsbuild, @Martin-Grunewald, @fwyzard can you please review it and eventually sign? Thanks. cms-bot commands are listed here |
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| outPFCandidates->emplace_back(MiniFloatConverter::float16to32(MiniFloatConverter::float32to16(cand.pt())), | ||
| MiniFloatConverter::float16to32(MiniFloatConverter::float32to16(cand.eta())), | ||
| MiniFloatConverter::float16to32(MiniFloatConverter::float32to16(cand.phi())), | ||
| MiniFloatConverter::float16to32(MiniFloatConverter::float32to16(cand.mass())), |
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is there no way to just truncate the precision, without converting to 16 bits and back to 32 bits ?
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of course there is: it is called bfloat16 (instead of halffloat)
https://en.wikipedia.org/wiki/Bfloat16_floating-point_format
BUT it really has low precision
bfloat16 is what it is mostly used for AI.
On Intel machines (AVX2 and more) one could use intrinsics to perform the conversion to/from halffloat (worth only if contiguous as in a SOA)
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Mhm, no, that doesn't seem like a good candidate here.
I just meant to ask if there is way to do MiniFloatConverter::float16to32(MiniFloatConverter::float32to16(x)) in a single call.
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under the assumption that the first call did not over/underflow it is trivial yes
(well, one must properly round, not truncate. still pretty trivial).
but at this point I do not understand what is going on, I was thinking data were stored in hf16 (aka int16), not in truncated float32
(ok I missed "let the compression reduce the information being stored.")
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but at this point I do not understand what is going on, I was thinking data were stored in hf16 (aka int16), not in truncated float32
that was my assumption as well
on the other hand, storing the truncated precision back in a float32 has the advantage of not affecting the data format, and apparently the compression is still good enough to reduce the size by ~37%
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sorry for the delay, I switched to MiniFloatConverter::reduceMantissaToNbitsRounding. And checked that the output matches the one from "MiniFloatConverter::float16to32(MiniFloatConverter::float32to16())" with 10 bits mantissa via Events->Scan(). The size is similar: I this is good then we can adjust the precision as we want. |
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+code-checks Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-29513/14954
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Pull request #29513 was updated. @cmsbuild, @Martin-Grunewald, @fwyzard can you please check and sign again. |
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This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @silviodonato, @dpiparo (and backports should be raised in the release meeting by the corresponding L2) |
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… point format
PR description:
As mentioned in a TSG on Jan. 15th:
https://indico.cern.ch/event/878772/contributions/3703563/attachments/1969842/3276766/ScoutingGroup.pdf
The PFScouting event size is reduced by 40% when PFCandidate 4-vectors are stored in Hal precision floating point format. I used the libminifloat class in CMSSW and convert back to float32 (the type returned by float32to16 is uint16_t) and let the compression reduce the information being stored.
PR validation:
I was running with and without the change and compared the output, and it looks the same. The per event size of the corresponding collection is indeed reduced after checking via edmEventSize.
File outputScoutingPF.root Events 10
Branch Name | Average Uncompressed Size (Bytes/Event) | Average Compressed Size (Bytes/Event)
float16: ScoutingParticles_hltScoutingPFPacker__HLT2018. 24530.5 7804.4
float32: ScoutingParticles_hltScoutingPFPacker__HLT2018. 24530.5 12444.5
if this PR is a backport please specify the original PR and why you need to backport that PR:
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