The linux kernel recently gained a new PSI meter, namely
a new /proc/pressure/irq meter has been added [1]:
full avg10=0.00 avg60=0.00 avg300=0.00 total=100648410
This commit adds support for this PSI meter by adding a
PressureStallIRQFullMeter_class.
[1] 52b1364ba0
`RichString_appendnAscii()` avoids a `strlen(3)` call over
` RichString_appendAscii()`.
Use the former where the length is available from a previous checked
`snprintf(3)` call.
Keep `RichString_appendAscii()` when passing a string literal and
rely on compilers to optimize the `strlen(3)` call away.
RichString_writeFrom takes a top spot during performance analysis due to the
calls to mbstowcs() and iswprint().
Most of the time we know in advance that we are only going to print regular
ASCII characters.
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.
Daniel Lange
Matthias Maier
mayurdahibhate
Christian Göttsche
Benny Baumann
Nathan Scott
Ran Benita