tor/changes/bug24613

  o Minor features (performance, 32-bit):
    - Improve performance on 32-bit systems by avoiding 64-bit division
      to calculate the current timestamp in milliseconds for channel
      padding computations. Implements ticket 24613.
Use monotime_coarse for transfer times and padding times Using absolute_msec requires a 64-bit division operation every time we calculate it, which gets expensive on 32-bit architectures. Instead, just use the lazy "monotime_coarse_get()" operation, and don't convert to milliseconds until we absolutely must. In this case, it seemed fine to use a full monotime_coarse_t rather than a truncated "stamp" as we did to solve this problem for the timerstamps in buf_t and packed_cell_t: There are vastly more cells and buffer chunks than there are channels, and using 16 bytes per channel in the worst case is not a big deal. There are still more millisecond operations here than strictly necessary; let's see any divisions show up in profiles. 2017-12-13 09:34:20 -05:00			`o Minor features (performance, 32-bit):`
			`- Improve performance on 32-bit systems by avoiding 64-bit division`
			`to calculate the current timestamp in milliseconds for channel`
			`padding computations. Implements ticket 24613.`