cmp: print verbose diffs as we find them#100
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oSoMoN merged 1 commit intouutils:mainfrom Oct 8, 2024
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Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #100 +/- ##
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+ Coverage 84.95% 85.11% +0.15%
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Files 12 12
Lines 5824 5818 -6
Branches 480 475 -5
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+ Hits 4948 4952 +4
+ Misses 856 846 -10
Partials 20 20
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Very nice optimization! I have a couple of minor suggestions, but this otherwise looks good to me. Thanks!
Before this change, we would first find all changes so we could obtain the largest offset we will report and use that to set up the padding. Now we use the file sizes to estimate the largest possible offset. Not only does this allow us to print earlier, reduces memory usage, as we do not store diffs to report later, but it also fixes a case in which our output was different to GNU cmp's - because it also seems to estimate based on size. Memory usage drops by a factor of 1000(!), without losing performance while comparing 2 binaries of hundreds of MBs: Before: Maximum resident set size (kbytes): 2489260 Benchmark 1: ../target/release/diffutils \ cmp -l -b /usr/lib64/chromium-browser/chromium-browser /usr/lib64/firefox/libxul.so Time (mean ± σ): 14.466 s ± 0.166 s [User: 12.367 s, System: 2.012 s] Range (min … max): 14.350 s … 14.914 s 10 runs After: Maximum resident set size (kbytes): 2636 Benchmark 1: ../target/release/diffutils \ cmp -l -b /usr/lib64/chromium-browser/chromium-browser /usr/lib64/firefox/libxul.so Time (mean ± σ): 13.724 s ± 0.038 s [User: 12.263 s, System: 1.372 s] Range (min … max): 13.667 s … 13.793 s 10 runs
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I was thinking of ways to further improve the code and began looking at memory usage, as I thought collecting the differences for verbose output could be problematic for larger files. I managed to rework the code to not incur more overhead, and we actually gain a little bit of performance with the lower memory usage.
Before this change, we would first find all changes so we could obtain the largest offset we will report and use that to set up the padding.
Now we use the file sizes to estimate the largest possible offset. Not only does this allow us to print earlier, reduces memory usage, as we do not store diffs to report later, but it also fixes a case in which our output was different to GNU cmp's - because it also seems to estimate based on size.
Memory usage drops by a factor of 1000(!), without losing performance while comparing 2 binaries of hundreds of MBs:
Before:
Maximum resident set size (kbytes): 2489260
Benchmark 1: ../target/release/diffutils
cmp -l -b /usr/lib64/chromium-browser/chromium-browser /usr/lib64/firefox/libxul.so
Time (mean ± σ): 14.466 s ± 0.166 s [User: 12.367 s, System: 2.012 s]
Range (min … max): 14.350 s … 14.914 s 10 runs
After:
Maximum resident set size (kbytes): 2636
Benchmark 1: ../target/release/diffutils
cmp -l -b /usr/lib64/chromium-browser/chromium-browser /usr/lib64/firefox/libxul.so
Time (mean ± σ): 13.724 s ± 0.038 s [User: 12.263 s, System: 1.372 s]
Range (min … max): 13.667 s … 13.793 s 10 runs