The pressure stall information (PSI) metrics provide useful information
on delays caused by waiting for CPU, IO and memory. Particularly on busy
servers it can provide a quick overview of what's "slowing things down".
This feature is supported on Linux >= 4.20.
The interface is documented here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/accounting/psi.txt
These links provide rationale:
https://lwn.net/Articles/759781/https://facebookmicrosites.github.io/psi/
The following metrics are added, corresponding to the currently exposed
lines (see `head /proc/pressure/*`):
- PressureStallCPUSome
- PressureStallIOSome
- PressureStallIOFull
- PressureStallMemorySome
- PressureStallMemoryFull
The color scheme is the same as that used for Load Average, however I
gave it separate entries just in case someone wants to change them
specifically.
Tested on 4.20.7-arch1-1-ARCH, on the linux platform.
Also tested that other platforms still compile (changed configure to use
the unsupported platform).
Closes#879.
Specifically, Platform_signals[] and Platform_numberOfSignals. Both are
not supposed to be mutable. Marking them 'const' puts them into rodata
sections in binary. And for Platform_numberOfSignals, this aids
optimization (aids only Link Time Optimization for now). :)
Signed-off-by: Kang-Che Sung <explorer09@gmail.com>
With the CLAMP macro replacing the combination of MIN and MAX, we will
have at least two advantages:
1. It's more obvious semantically.
2. There are no more mixes of confusing uses like MIN(MAX(a,b),c) and
MAX(MIN(a,b),c) and MIN(a,MAX(b,c)) appearing everywhere. We unify
the 'clamping' with a single macro.
Note that the behavior of this CLAMP macro is different from
the combination `MAX(low,MIN(x,high))`.
* This CLAMP macro expands to two comparisons instead of three from
MAX and MIN combination. In theory, this makes the code slightly
smaller, in case that (low) or (high) or both are computed at
runtime, so that compilers cannot optimize them. (The third
comparison will matter if (low)>(high); see below.)
* CLAMP has a side effect, that if (low)>(high) it will produce weird
results. Unlike MIN & MAX which will force either (low) or (high) to
win. No assertion of ((low)<=(high)) is done in this macro, for now.
This CLAMP macro is implemented like described in glib
<http://developer.gnome.org/glib/stable/glib-Standard-Macros.html>
and does not handle weird uses like CLAMP(a++, low++, high--) .
Implementations for Linux (tested) and FreeBSD (still untested, thanks to @etosan for providing the table).
Darwin and OpenBSD(ping @mmcco) builds should be broken now, pending their own tables.
