Performance improvement for libcudf upper/lower conversion for long strings

[davidwendt]

Description

Improves on performance for longer strings with cudf::strings::to_lower() cudf::strings::to_upper() and cudf::strings::swapcase() APIs.

The current implementation works well with smallish strings and so this new implementation splits into a longish string algorithm when average number of bytes per string is 64 bytes or greater. The new implementation is similar but computes the output size of each string with a warp per string function. In addition, a check is added for long strings testing if all bytes are ASCII and thereby can run a faster kernel for this case.

Reference #13048

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[davidwendt]

Some benchmarks used to help find the proper threshold

UTF-8 encoded

|  width  |  num_rows  |   Ref Time |   Cmp Time |          Diff |   %Diff |
|---------|------------|------------|------------|---------------|---------|
|   32    |    4096    | 139.464 us | 140.954 us |      1.490 us |   1.07% |
|   48    |    4096    | 158.875 us | 158.903 us |      0.028 us |   0.02% |
|   64    |    4096    | 176.689 us | 179.506 us |      2.817 us |   1.59% |
|   80    |    4096    | 199.294 us | 200.059 us |      0.765 us |   0.38% |
|   96    |    4096    | 218.589 us | 222.201 us |      3.612 us |   1.65% |
|   112   |    4096    | 240.699 us | 241.845 us |      1.146 us |   0.48% |
|   128   |    4096    | 261.917 us | 225.478 us |    -36.439 us | -13.91% |
|   144   |    4096    | 285.389 us | 236.887 us |    -48.501 us | -16.99% |
|   160   |    4096    | 305.034 us | 250.683 us |    -54.351 us | -17.82% |
|   176   |    4096    | 334.522 us | 265.868 us |    -68.654 us | -20.52% |
|   192   |    4096    | 357.492 us | 282.691 us |    -74.800 us | -20.92% |
|   208   |    4096    | 373.461 us | 288.581 us |    -84.880 us | -22.73% |
|   224   |    4096    | 400.474 us | 307.051 us |    -93.423 us | -23.33% |
|   240   |    4096    | 426.321 us | 320.548 us |   -105.772 us | -24.81% |
|   256   |    4096    | 443.517 us | 331.745 us |   -111.773 us | -25.20% |
|   272   |    4096    | 471.975 us | 345.760 us |   -126.216 us | -26.74% |
|   284   |    4096    | 490.323 us | 359.025 us |   -131.298 us | -26.78% |
|   300   |    4096    | 506.685 us | 366.929 us |   -139.756 us | -27.58% |
|   32    |   32768    | 143.739 us | 144.959 us |      1.221 us |   0.85% |
|   48    |   32768    | 164.004 us | 163.662 us |     -0.341 us |  -0.21% |
|   64    |   32768    | 334.301 us | 320.952 us |    -13.350 us |  -3.99% |
|   80    |   32768    | 360.091 us | 346.512 us |    -13.579 us |  -3.77% |
|   96    |   32768    | 387.552 us | 371.259 us |    -16.293 us |  -4.20% |
|   112   |   32768    | 390.625 us | 391.448 us |      0.823 us |   0.21% |
|   128   |   32768    | 413.678 us | 416.810 us |      3.131 us |   0.76% |
|   144   |   32768    | 441.454 us | 415.916 us |    -25.538 us |  -5.79% |
|   160   |   32768    | 464.721 us | 430.787 us |    -33.934 us |  -7.30% |
|   176   |   32768    | 493.800 us | 449.489 us |    -44.310 us |  -8.97% |
|   192   |   32768    | 520.755 us | 465.078 us |    -55.677 us | -10.69% |
|   208   |   32768    | 541.959 us | 479.342 us |    -62.617 us | -11.55% |
|   224   |   32768    | 570.302 us | 497.108 us |    -73.194 us | -12.83% |
|   240   |   32768    | 602.929 us | 516.911 us |    -86.018 us | -14.27% |
|   256   |   32768    | 615.334 us | 529.682 us |    -85.651 us | -13.92% |
|   272   |   32768    | 647.557 us | 552.137 us |    -95.421 us | -14.74% |
|   284   |   32768    | 670.339 us | 565.372 us |   -104.967 us | -15.66% |
|   300   |   32768    | 691.753 us | 579.555 us |   -112.198 us | -16.22% |
|   32    |   262144   | 368.272 us | 365.435 us |     -2.837 us |  -0.77% |
|   48    |   262144   | 452.968 us | 455.215 us |      2.247 us |   0.50% |
|   64    |   262144   | 568.695 us | 573.062 us |      4.366 us |   0.77% |
|   80    |   262144   | 821.041 us | 800.553 us |    -20.489 us |  -2.50% |
|   96    |   262144   |   1.203 ms |   1.201 ms |     -1.299 us |  -0.11% |
|   112   |   262144   |   1.712 ms |   1.707 ms |     -4.889 us |  -0.29% |
|   128   |   262144   |   2.213 ms |   2.296 ms |     82.105 us |   3.71% |
|   144   |   262144   |   2.808 ms |   2.876 ms |     68.463 us |   2.44% |
|   160   |   262144   |   3.319 ms |   3.366 ms |     47.901 us |   1.44% |
|   176   |   262144   |   4.018 ms |   3.957 ms |    -61.271 us |  -1.52% |
|   192   |   262144   |   4.815 ms |   4.594 ms |   -220.492 us |  -4.58% |
|   208   |   262144   |   5.850 ms |   5.299 ms |   -550.946 us |  -9.42% |
|   224   |   262144   |   6.618 ms |   5.920 ms |   -697.494 us | -10.54% |
|   240   |   262144   |   7.591 ms |   6.596 ms |   -995.731 us | -13.12% |
|   256   |   262144   |   8.731 ms |   7.331 ms |  -1399.589 us | -16.03% |
|   272   |   262144   |   9.352 ms |   8.039 ms |  -1312.864 us | -14.04% |
|   284   |   262144   |  10.186 ms |   8.674 ms |  -1511.643 us | -14.84% |
|   300   |   262144   |  10.985 ms |   9.464 ms |  -1520.345 us | -13.84% |
|   32    |  2097152   |   2.123 ms |   2.114 ms |     -9.057 us |  -0.43% |
|   48    |  2097152   |   2.964 ms |   2.966 ms |      1.893 us |   0.06% |
|   64    |  2097152   |   3.635 ms |   3.638 ms |      2.645 us |   0.07% |
|   80    |  2097152   |   4.801 ms |   4.888 ms |     86.769 us |   1.81% |
|   96    |  2097152   |   7.525 ms |   7.547 ms |     22.433 us |   0.30% |
|   112   |  2097152   |  11.871 ms |  11.857 ms |    -13.990 us |  -0.12% |
|   128   |  2097152   |  16.668 ms |  16.709 ms |     40.598 us |   0.24% |
|   144   |  2097152   |  20.803 ms |  21.075 ms |    271.984 us |   1.31% |
|   160   |  2097152   |  25.761 ms |  25.832 ms |     71.071 us |   0.28% |
|   176   |  2097152   |  31.161 ms |  31.113 ms |    -47.389 us |  -0.15% |
|   192   |  2097152   |  36.495 ms |  36.719 ms |    223.964 us |   0.61% |
|   208   |  2097152   |  42.361 ms |  42.323 ms |    -38.315 us |  -0.09% |
|   224   |  2097152   |  48.315 ms |  47.921 ms |   -394.147 us |  -0.82% |
|   240   |  2097152   |  54.518 ms |  53.334 ms |  -1183.929 us |  -2.17% |
|   256   |  2097152   |  61.370 ms |  58.930 ms |  -2440.378 us |  -3.98% |
|   272   |  2097152   |  67.845 ms |  63.620 ms |  -4224.839 us |  -6.23% |
|   284   |  2097152   |  72.688 ms |  67.802 ms |  -4885.784 us |  -6.72% |
|   300   |  2097152   |  78.890 ms |  73.347 ms |  -5542.819 us |  -7.03% |

Also some ASCII-only benchmark results for fun.

ASCII encoded

|  width  |  num_rows  |   Ref Time |   Cmp Time |          Diff |   %Diff |
|---------|------------|------------|------------|---------------|---------|
|   32    |    4096    | 139.478 us | 142.197 us |      2.719 us |   1.95% |
|   48    |    4096    | 161.565 us | 163.331 us |      1.767 us |   1.09% |
|   64    |    4096    | 181.692 us | 183.175 us |      1.483 us |   0.82% |
|   80    |    4096    | 204.902 us | 206.413 us |      1.511 us |   0.74% |
|   96    |    4096    | 228.466 us | 230.612 us |      2.145 us |   0.94% |
|   112   |    4096    | 253.778 us | 254.149 us |      0.371 us |   0.15% |
|   128   |    4096    | 275.308 us | 112.322 us |   -162.985 us | -59.20% |
|   144   |    4096    | 304.149 us | 111.397 us |   -192.751 us | -63.37% |
|   160   |    4096    | 327.739 us | 111.962 us |   -215.777 us | -65.84% |
|   176   |    4096    | 355.701 us | 113.248 us |   -242.453 us | -68.16% |
|   192   |    4096    | 386.597 us | 115.851 us |   -270.746 us | -70.03% |
|   208   |    4096    | 406.453 us | 114.336 us |   -292.117 us | -71.87% |
|   224   |    4096    | 432.067 us | 115.240 us |   -316.827 us | -73.33% |
|   240   |    4096    | 460.123 us | 114.714 us |   -345.409 us | -75.07% |
|   256   |    4096    | 484.789 us | 115.387 us |   -369.402 us | -76.20% |
|   272   |    4096    | 511.011 us | 115.030 us |   -395.981 us | -77.49% |
|   284   |    4096    | 529.764 us | 115.128 us |   -414.636 us | -78.27% |
|   300   |    4096    | 709.508 us | 254.920 us |   -454.588 us | -64.07% |
|   32    |   32768    | 144.803 us | 146.937 us |      2.134 us |   1.47% |
|   48    |   32768    | 323.522 us | 305.653 us |    -17.869 us |  -5.52% |
|   64    |   32768    | 187.701 us | 188.913 us |      1.213 us |   0.65% |
|   80    |   32768    | 353.027 us | 351.905 us |     -1.122 us |  -0.32% |
|   96    |   32768    | 378.826 us | 379.770 us |      0.944 us |   0.25% |
|   112   |   32768    | 406.792 us | 408.756 us |      1.963 us |   0.48% |
|   128   |   32768    | 430.999 us | 433.291 us |      2.293 us |   0.53% |
|   144   |   32768    | 454.199 us | 263.664 us |   -190.534 us | -41.95% |
|   160   |   32768    | 481.146 us | 266.852 us |   -214.294 us | -44.54% |
|   176   |   32768    | 510.508 us | 267.896 us |   -242.612 us | -47.52% |
|   192   |   32768    | 540.338 us | 267.730 us |   -272.608 us | -50.45% |
|   208   |   32768    | 567.150 us | 269.128 us |   -298.023 us | -52.55% |
|   224   |   32768    | 593.716 us | 270.425 us |   -323.291 us | -54.45% |
|   240   |   32768    | 621.767 us | 271.241 us |   -350.526 us | -56.38% |
|   256   |   32768    | 645.887 us | 272.587 us |   -373.300 us | -57.80% |
|   272   |   32768    | 681.750 us | 283.170 us |   -398.580 us | -58.46% |
|   284   |   32768    | 701.165 us | 284.398 us |   -416.767 us | -59.44% |
|   300   |   32768    | 730.564 us | 287.202 us |   -443.362 us | -60.69% |
|   32    |   262144   | 374.509 us | 374.713 us |      0.204 us |   0.05% |
|   48    |   262144   | 466.607 us | 467.701 us |      1.094 us |   0.23% |
|   64    |   262144   | 591.481 us | 611.986 us |     20.505 us |   3.47% |
|   80    |   262144   | 827.996 us | 832.720 us |      4.724 us |   0.57% |
|   96    |   262144   |   1.237 ms |   1.253 ms |     15.853 us |   1.28% |
|   112   |   262144   |   1.801 ms |   1.785 ms |    -16.051 us |  -0.89% |
|   128   |   262144   |   2.388 ms | 595.482 us |  -1792.254 us | -75.06% |
|   144   |   262144   |   2.972 ms | 663.376 us |  -2308.238 us | -77.68% |
|   160   |   262144   |   3.607 ms | 730.779 us |  -2875.985 us | -79.74% |
|   176   |   262144   |   4.345 ms | 793.734 us |  -3551.176 us | -81.73% |
|   192   |   262144   |   5.127 ms | 858.045 us |  -4268.581 us | -83.26% |
|   208   |   262144   |   6.367 ms | 923.390 us |  -5443.978 us | -85.50% |
|   224   |   262144   |   7.250 ms | 988.587 us |  -6261.502 us | -86.36% |
|   240   |   262144   |   8.354 ms |   1.052 ms |  -7301.612 us | -87.40% |
|   256   |   262144   |   9.291 ms |   1.115 ms |  -8175.324 us | -88.00% |
|   272   |   262144   |  10.203 ms |   1.181 ms |  -9021.873 us | -88.43% |
|   284   |   262144   |  10.893 ms |   1.242 ms |  -9650.689 us | -88.60% |
|   300   |   262144   |  11.821 ms |   1.306 ms | -10515.608 us | -88.95% |
|   32    |  2097152   |   2.145 ms |   2.136 ms |     -8.898 us |  -0.41% |
|   48    |  2097152   |   3.021 ms |   3.004 ms |    -17.131 us |  -0.57% |
|   64    |  2097152   |   3.716 ms |   3.668 ms |    -47.992 us |  -1.29% |
|   80    |  2097152   |   4.933 ms |   4.976 ms |     43.159 us |   0.87% |
|   96    |  2097152   |   7.588 ms |   7.620 ms |     32.803 us |   0.43% |
|   112   |  2097152   |  12.018 ms |  12.187 ms |    168.769 us |   1.40% |
|   128   |  2097152   |  17.037 ms |   4.520 ms | -12517.386 us | -73.47% |
|   144   |  2097152   |  21.979 ms |   3.874 ms | -18105.243 us | -82.37% |
|   160   |  2097152   |  27.158 ms |   4.271 ms | -22887.534 us | -84.27% |
|   176   |  2097152   |  32.809 ms |   4.668 ms | -28141.898 us | -85.77% |
|   192   |  2097152   |  38.495 ms |   5.024 ms | -33471.669 us | -86.95% |
|   208   |  2097152   |  44.596 ms |   5.411 ms | -39184.793 us | -87.87% |
|   224   |  2097152   |  50.967 ms |   5.246 ms | -45721.448 us | -89.71% |
|   240   |  2097152   |  58.064 ms |   5.246 ms | -52818.466 us | -90.97% |
|   256   |  2097152   |  65.177 ms |   5.980 ms | -59197.256 us | -90.82% |
|   272   |  2097152   |  72.123 ms |   8.408 ms | -63715.670 us | -88.34% |
|   284   |  2097152   |  77.502 ms |   7.803 ms | -69699.548 us | -89.93% |
|   300   |  2097152   |  85.013 ms |   7.721 ms | -77292.000 us | -90.92% |

[karthikeyann]

LGTM 👍

[davidwendt]

/merge