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viml/profile: switch to uv_gettimeofday() #10356

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Performance of high-resolution time (clock_gettime via uv_hrtime) is
expensive on some systems.  For profiling VimL, syntax, etc., we don't
care about nanosecond-precision and monotonicity edge-cases, so avoid
uv_hrtime().

closes #10328

From the uv__hrtime() source:
0cdb4a5b4b/src/unix/linux-core.c (L442-L462)

    /* Prefer CLOCK_MONOTONIC_COARSE if available but only when it has
     * millisecond granularity or better.  CLOCK_MONOTONIC_COARSE is
     * serviced entirely from the vDSO, whereas CLOCK_MONOTONIC may
     * decide to make a costly system call.
     */

This micro-benchmark (Debug build) shows negligible differences on my
system:

    #include <sys/time.h>
    ...

    proftime_T tm = profile_start();
    int trials = 999999;
    int64_t t = 0;
    struct timeval tv;
    for (int i = 0; i < trials; i++) {
      t += gettimeofday(&tv,NULL);
    }
    tm = profile_end(tm);
    ILOG("%d trials of gettimeofday: %s", trials, profile_msg(tm));
    tm = profile_start();
    for (int i = 0; i < trials; i++) {
      t += os_hrtime();
    }
    tm = profile_end(tm);
    ILOG("%d trials of os_hrtime: %s", trials, profile_msg(tm));
    tm = profile_start();
    for (int i = 0; i < trials; i++) {
      t += os_utime();
    }
    tm = profile_end(tm);
    ILOG("%d trials of os_utime: %s", trials, profile_msg(tm));
    ILOG("%zu", t);
This commit is contained in:
Justin M. Keyes
2019-06-29 16:39:22 +02:00
committed by GitHub
parent 23a9794920
commit e2ce5ff9d6
4 changed files with 84 additions and 50 deletions
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7
src/nvim/assert.h
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@@ -133,8 +133,10 @@
/// Alternative for compilers without __builtin_xx_overflow ?
/// https://stackoverflow.com/a/44830670/152142
///
/// @param MAX Maximum value of the narrowest type of operand.
/// Not used if compiler supports __builtin_add_overflow.
/// @param a Operand 1.
/// @param b Operand 2.
/// @param c Where to store the result.
/// @param t Result type. Not used if compiler supports __builtin_add_overflow.
#ifdef HAVE_BUILTIN_ADD_OVERFLOW
# define STRICT_ADD(a, b, c, t) \
do { \
@@ -150,6 +152,7 @@
/// @def STRICT_SUB
/// @brief Subtracts (a - b) and stores result in `c`. Aborts on overflow.
/// @see STRICT_ADD
#ifdef HAVE_BUILTIN_ADD_OVERFLOW
# define STRICT_SUB(a, b, c, t) \
do { \