branch master updated: doc: guix-days-2024: Add notes from the profiling discussion.

[Ludovic Courtès]

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commit b7462f58b3bda2d24747e73eefdaf24805b921bf
Author: Adriel Dumas--Jondeau <leirda@disroot.org>
AuthorDate: Tue Feb 6 10:36:11 2024 +0100

    doc: guix-days-2024: Add notes from the profiling discussion.
    
    Change-Id: I57abb36cbab43010f43270e626087cb2cb211c14
    Signed-off-by: Ludovic Courtès <ludo@gnu.org>
---
 doc/guix-days-2024/profiling.md | 81 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/doc/guix-days-2024/profiling.md b/doc/guix-days-2024/profiling.md
new file mode 100644
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+++ b/doc/guix-days-2024/profiling.md
@@ -0,0 +1,81 @@
+# What is profiling?
+
+- Have an idea of the execution time of part of code
+- Have some kind of flame graph
+- What feels slow (not necessarily what is slow)
+- Where's RAM most used?
+
+# What should be profiled?
+
+- guix authenticate
+- guix system/home
+- guix pull
+- not the compilation itself
+- Guix system start time (like ~systemd-analyse~)
+- Time of deployments
+
+# Why?
+
+- To be able to use Guix on low-end/older devices
+- Building a package is long (because of compilation)
+- Pulling is slow (because of network)
+- Computing Guix derivations (guix system init/reconfigure)
+- Authenticating guix commits (especially with many/big commits)
+
+- It's compelling (for HPC people for instance)
+
+- To know where there's progress to be made
+- ~make~ in the Guix repo is slow so testing is not as immediate as it could be
+- As small/fast finale binary as possible
+- To get a feel of what specs are needed to do actual stuff
+
+# How?
+
+- Guile has ~trace~ / ~profile~ procedure that you could use on Guix procs
+  - How to make a flame graph from this data or any other format?
+- Retrieving some metrics on demand from build systems (via ~guix build~)
+  - to get logs RAM/space/temporal usage during compilation
+- Profiling daemons resources usage from shepherd (exposing those profiling 
options to users)
+- Making shepherd services to profile ~guix shell --container~
+
+# Starting point
+
+```
+$ guix repl
+(guix-user)> ,use (guix scripts build)
+(guix-user)> ,profile (guix-build "hello")
+%     cumulative   self             
+time   seconds     seconds  procedure
+ 24.00      0.16      0.16  put-string
+ 16.00      0.11      0.11  write
+ 12.00      0.11      0.08  append
+ 12.00      0.08      0.08  get-bytevector-n
+  4.00      0.05      0.03  guix/gexp.scm:809:0:gexp-attribute
+  4.00      0.03      0.03  string->utf8
+  4.00      0.03      0.03  guix/packages.scm:1969:0:package->derivation
+  4.00      0.03      0.03  regexp-exec
+  4.00      0.03      0.03  cons
+  4.00      0.03      0.03  guix/store.scm:1426:4
+  4.00      0.03      0.03  apply-smob/1
+  4.00      0.03      0.03  sort
+(guix-user)> ,trace (guix-build "hello") ; doesn't output any trace for some 
reason
+/gnu/store/6fbh8phmp3izay6c0dpggpxhcjn4xlm5-hello-2.12.1
+(guix-user)> ^D
+$ guile
+(guile-user)> ,use (guix scripts build)
+(guile-user)> ,trace (guix-build "hello") ; however it does work
+trace: |  (guix-build "hello")
+trace: |  |  (_ (guix scripts) #:ensure #f)
+trace: |  |  (_ #<procedure 7ff4802c5000 at ice-9/boot-9.scm:3241:7 ()>)
+trace: |  |  |  (lock-mutex #<mutex 7ff487d01fc0>)
+...
+trace: |  |  |  |  |  |  (fileno #<output: file /dev/pts/3>)
+trace: |  |  |  |  |  |  1
+trace: |  |  |  |  |  |  (bytevector->pointer@system/foreign #vu8(0 0 0 0 0 0 
0 0))
+trace: |  |  |  |  |  |  (bytevector->pointer #vu8(0 0 0 0 0 0 0 0))
+trace: |  |  |  |  |  |  #<pointer 0x7ff48036a7d0>
+```
+
+```sh
+$ guix build --verbosity=<big number> --debug=<big number>
+```