dotfiles: record what VTune gives a standard user

Measured on this box as latislab\claude, unelevated: vtune -collect hotspots
runs a full collection and finalization, exit 0.  Hardware event-based sampling
does not -- VTune warns "To collect microarchitecture performance insights, run
the product as administrator" at the top of every unelevated run, and
uarch-exploration and hotspots -knob sampling-mode=hw both fail.  Which matches
Intel's own documentation: a regular user on Windows gets the User-Mode Sampling
analyses and nothing else.

Worth writing down because of how the failure presents: "cannot recognize the
processor", which reads like unsupported hardware and is not.  This is a Kaby
Lake i5-8350U and the sampling drivers (sepdrv5, sepdal, vtss) are installed and
running; VTune identifies the PMU through them and cannot reach them
unelevated.  That last step is inference from the evidence rather than something
confirmed - confirming it takes one elevated run.

And unlike the ETW work in this branch there is no group to join: the Linux
sampling driver can be handed to a vtune group, but on Windows the documented
answer is to elevate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YMh8i2QzkHNdE3MkKfcaT6

diff --git a/README.md b/README.md
index e0ef7448f859dff7eab6d24cfd958452896b292b..1bdadcac083ea54d6324235b6e6f549f849fb0f6 100644 (file)
--- a/README.md
+++ b/README.md
@@ -151,6 +151,18 @@ throwaway VM reachable from a Linux host.
   intel-vtune-<version>_offline.exe -a --silent --cli --eula accept
   ```
 
+  **Running it needs no elevation, but hardware sampling does.** A standard user
+  gets the User-Mode Sampling analyses — `vtune -collect hotspots` and threading
+  — and they work: measured here, collection and finalization, exit 0. Hardware
+  event-based sampling (`uarch-exploration`, `memory-access`, `hotspots -knob
+  sampling-mode=hw`) wants administrator, and VTune says so in a warning at the
+  top of every unelevated run. Note the failure it actually gives is *"cannot
+  recognize the processor"*, which reads like a hardware problem and is not one:
+  the drivers (`sepdrv5`, `sepdal`, `vtss`) are installed and running, and VTune
+  identifies the PMU through them. Unlike ETW there is no group to join for this
+  — the Linux driver can be handed to a `vtune` group, but on Windows the
+  documented answer is to run as administrator.
+
 - **Tracing without a UAC prompt.** `xperf` and `wpr` fail for a standard user in
   two different ways, because two different things are missing: