diff options
| author | Alan Somers <asomers@FreeBSD.org> | 2022-05-06 00:35:23 +0300 |
|---|---|---|
| committer | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2022-07-11 14:19:29 +0300 |
| commit | 27dfb5f33fa4954f6278ae8b82584c269fb6e6ef (patch) | |
| tree | 57a6ff730d286498d0bd005985bdfcf34c3b1d12 /newlib/libc/sys | |
| parent | 0ed668df2cdd29abfb94de726745e43243c787d0 (diff) | |
Correctly measure system load averages > 1024
The old fixed-point arithmetic used for calculating load averages had an
overflow at 1024. So on systems with extremely high load, the observed
load average would actually fall back to 0 and shoot up again, creating
a kind of sawtooth graph.
Fix this by using 64-bit math internally, while still reporting the load
average to userspace as a 32-bit number.
Sponsored by: Axcient
Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D35134
Diffstat (limited to 'newlib/libc/sys')
| -rw-r--r-- | newlib/libc/sys/rtems/include/sys/param.h | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/newlib/libc/sys/rtems/include/sys/param.h b/newlib/libc/sys/rtems/include/sys/param.h index c346453bf..9596ecf52 100644 --- a/newlib/libc/sys/rtems/include/sys/param.h +++ b/newlib/libc/sys/rtems/include/sys/param.h @@ -248,12 +248,12 @@ * Scale factor for scaled integers used to count %cpu time and load avgs. * * The number of CPU `tick's that map to a unique `%age' can be expressed - * by the formula (1 / (2 ^ (FSHIFT - 11))). The maximum load average that - * can be calculated (assuming 32 bits) can be closely approximated using - * the formula (2 ^ (2 * (16 - FSHIFT))) for (FSHIFT < 15). + * by the formula (1 / (2 ^ (FSHIFT - 11))). Since the intermediate + * calculation is done with 64-bit precision, the maximum load average that can + * be calculated is approximately 2^32 / FSCALE. * * For the scheduler to maintain a 1:1 mapping of CPU `tick' to `%age', - * FSHIFT must be at least 11; this gives us a maximum load avg of ~1024. + * FSHIFT must be at least 11. This gives a maximum load avg of 2 million. */ #define FSHIFT 11 /* bits to right of fixed binary point */ #define FSCALE (1<<FSHIFT) |