[newlib-cygwin] Correctly measure system load averages > 1024

[newlib-cygwin] Correctly measure system load averages > 1024

[Sebastian Huber]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=27dfb5f33fa4954f6278ae8b82584c269fb6e6ef

commit 27dfb5f33fa4954f6278ae8b82584c269fb6e6ef
Author: Alan Somers <asomers@FreeBSD.org>
Date:   Thu May 5 15:35:23 2022 -0600

    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

Diff:
---
 newlib/libc/sys/rtems/include/sys/param.h | 8 ++++----
 1 file 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)