Add an override to avoid using --kcore

Signed-off-by: Tudor Brindus <[email protected]>
janestreet · Jun 4, 2024 · 42b7c90 · 42b7c90
1 parent 78aa314
commit 42b7c90
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Showing 3 changed files with 27 additions and 18 deletions.
diff --git a/src/env_vars.ml b/src/env_vars.ml
@@ -15,6 +15,9 @@ let perf_path = Option.value ~default:"perf" (Unix.getenv "MAGIC_TRACE_PERF_PATH
    checks around kernel tracing when not root. *)
 let perf_is_privileged = Option.is_some (Unix.getenv "MAGIC_TRACE_PERF_IS_PRIVILEGED")
 
+(** Override whether kcore will be used (in the case that [perf] supports it at all). *)
+let perf_no_kcore = Option.is_some (Unix.getenv "MAGIC_TRACE_PERF_NO_KCORE")
+
 (* Turns on hidden command line options and attached "[inferred start time]" to functions
    with inferred start times.
 

diff --git a/src/env_vars.mli b/src/env_vars.mli
@@ -4,6 +4,7 @@ val debug : bool
 val experimental : bool
 val perf_path : string
 val perf_is_privileged : bool
+val perf_no_kcore : bool
 val perfetto_dir : string option
 val no_dlfilter : bool
 val fzf_demangle_symbols : bool
diff --git a/src/perf_tool_backend.ml b/src/perf_tool_backend.ml
@@ -319,24 +319,29 @@ module Recording = struct
       |> Deferred.return
     in
     let kcore_opts =
-      match
-        collection_mode, trace_scope, Perf_capabilities.(do_intersect capabilities kcore)
-      with
-      | Intel_processor_trace _, Userspace, _ | Stacktrace_sampling _, _, _ -> []
-      | Intel_processor_trace _, (Kernel | Userspace_and_kernel), true -> [ "--kcore" ]
-      | Intel_processor_trace _, (Kernel | Userspace_and_kernel), false ->
-        (* Strictly speaking, we could recreate tools/perf/perf-with-kcore.sh
-           here instead of bailing. But that's tricky, and upgrading to a newer
-           perf is easier. *)
-        Core.eprintf
-          "Warning: old perf version detected! perf userspace tools v5.5 contain an \
-           important feature, kcore, that make decoding kernel traces more reliable. In \
-           our experience, tracing the kernel mostly works without this feature, but you \
-           may run into problems if you're trying to trace through self-modifying code \
-           (the kernel may do this more than you think). Install a perf version >= 5.5 \
-           to avoid this.\n\
-           %!";
-        []
+      if Env_vars.perf_no_kcore
+      then []
+      else (
+        match
+          ( collection_mode
+          , trace_scope
+          , Perf_capabilities.(do_intersect capabilities kcore) )
+        with
+        | Intel_processor_trace _, Userspace, _ | Stacktrace_sampling _, _, _ -> []
+        | Intel_processor_trace _, (Kernel | Userspace_and_kernel), true -> [ "--kcore" ]
+        | Intel_processor_trace _, (Kernel | Userspace_and_kernel), false ->
+          (* Strictly speaking, we could recreate tools/perf/perf-with-kcore.sh
+             here instead of bailing. But that's tricky, and upgrading to a newer
+             perf is easier. *)
+          Core.eprintf
+            "Warning: old perf version detected! perf userspace tools v5.5 contain an \
+             important feature, kcore, that make decoding kernel traces more reliable. \
+             In our experience, tracing the kernel mostly works without this feature, \
+             but you may run into problems if you're trying to trace through \
+             self-modifying code (the kernel may do this more than you think). Install a \
+             perf version >= 5.5 to avoid this.\n\
+             %!";
+          [])
     in
     let snapshot_size_opt =
       match snapshot_size, collection_mode with