From 27dfb5f33fa4954f6278ae8b82584c269fb6e6ef Mon Sep 17 00:00:00 2001 From: Alan Somers Date: Thu, 5 May 2022 15:35:23 -0600 Subject: 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 --- newlib/libc/sys/rtems/include/sys/param.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'newlib') diff --git a/newlib/libc/sys/rtems/include/sys/param.h b/newlib/libc/sys/rtems/include/sys/param.h index c346453..9596ecf 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<