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unsnap: busy wait a number of cycles #8073

Merged
merged 4 commits into from
Apr 28, 2021
Merged

unsnap: busy wait a number of cycles #8073

merged 4 commits into from
Apr 28, 2021

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vuule
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@vuule vuule commented Apr 27, 2021

Busy replacement for nanosleep.

@github-actions github-actions bot added the libcudf Affects libcudf (C++/CUDA) code. label Apr 27, 2021
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codecov bot commented Apr 27, 2021 •
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Codecov Report

Merging #8073 (6ea88b0) into branch-0.19 (bbeb2aa) will not change coverage.
The diff coverage is n/a.

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@@             Coverage Diff              @@
##           branch-0.19    #8073   +/-   ##
============================================
  Coverage        82.74%   82.74%           
============================================
  Files              103      103           
  Lines            17702    17702           
============================================
  Hits             14648    14648           
  Misses            3054     3054

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harrism
harrism approved these changes Apr 27, 2021
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Minor suggestions. Otherwise looks fine.

cpp/src/io/comp/unsnap.cu
@@ -280,7 +291,7 @@ __device__ void snappy_decode_symbols(unsnap_state_s *s, uint32_t t)
if (t == 0) {
s->q.prefetch_rdpos = cur;
#pragma unroll(1) // We don't want unrolling here
while (s->q.prefetch_wrpos < min(cur + 5 * batch_size, end)) {}
while (s->q.prefetch_wrpos < min(cur + 5 * batch_size, end)) { busy_wait(10); }
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Why 10 in some places and 20 in others?

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The original times in nanoseconds were 50 or 100. I noticed a significant perf regression when using the same number of cycles (compared to no waits). Divided all wait cycles by 5 and got great perf results. Went with this to make the PR available for testing ASAP.
In short, the numbers are not carefully chosen, I'm open to suggestions on the values to use here.

@harrism harrism added ! - Hotfix Hotfix is a bug that affects the majority of users for which there is no reasonable workaround bug Something isn't working non-breaking Non-breaking change labels Apr 27, 2021
vuule and others added 2 commits April 27, 2021 15:41
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With this change, the hang reported #8055 is not seen anymore. We've tested small batches of queries, and last night triggered a much wider run and didn't see issues. So far so good @vuule.

@vuule vuule marked this pull request as ready for review April 28, 2021 16:50
@vuule vuule requested a review from a team as a code owner April 28, 2021 16:50
@vuule vuule requested review from cwharris and codereport and removed request for a team April 28, 2021 16:50
@sameerz sameerz linked an issue Apr 28, 2021 that may be closed by this pull request
[BUG] Removal of nanosleep causes regression in RAPIDS Accelerator for Apache Spark #8055
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@raydouglass raydouglass merged commit 2a82eca into rapidsai:branch-0.19 Apr 28, 2021
@sameerz sameerz mentioned this pull request Apr 29, 2021
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@andygrove andygrove mentioned this pull request May 4, 2021
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@vuule vuule deleted the bug-unsnap-busy-wait branch April 20, 2022 23:47
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@harrism harrism harrism approved these changes

@devavret devavret devavret approved these changes

@elstehle elstehle elstehle approved these changes

@cwharris cwharris Awaiting requested review from cwharris

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[BUG] Removal of nanosleep causes regression in RAPIDS Accelerator for Apache Spark
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@vuule @abellina @harrism @devavret @elstehle @raydouglass