add duration metric, tolerate missing tracepoints, ship el8 build

- Bubbles, treemap, icicle, and the live flamegraph 'b' cycle now include
  syscall duration (sum) as a third metric alongside events and bytes.
  Statsengine snapshots expose TotalLatencyNs to support this.
- AttachAll takes an optional warn callback. Production passes one so older
  kernels that lack newer tracepoints log a warning and keep going instead
  of aborting startup.
- Dockerfile.el8 + scripts/build-with-docker-el8.sh + mage buildDockerEl8
  produce ior.el8, a static binary built against Rocky Linux 8 glibc for
  RHEL/Rocky/Alma 8 hosts.
- README.md documents installing mage and the new el8 target.

1 files changed, 19 insertions, 0 deletions

diff --git a/README.md b/README.md
index 6b4de45..4c9ca05 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,18 @@ The demo is fully reproducible: `mage installDemoTools` once, then `sudo -v && m
 ## Requirements
 
 - Docker and a Linux host with a BTF-enabled kernel (`/sys/kernel/btf/vmlinux` present).
+- Go (any 1.x version on `PATH`) for installing the [Mage](https://magefile.org) build tool.
+
+## Install Mage
+
+The build orchestration uses Mage. Install the `mage` binary once before any of
+the build commands below:
+
+```shell
+go install github.com/magefile/mage@latest
+```
+
+Make sure `$(go env GOPATH)/bin` (typically `$HOME/go/bin`) is on your `PATH`.
 
 ## Build
 
@@ -48,6 +60,13 @@ cached image and finish in under a minute. To skip the image rebuild:
 ./scripts/build-with-docker.sh --run
 ```
 
+To target hosts with the older glibc on RHEL/Rocky/Alma 8, build a sibling
+binary called `ior.el8` from a Rocky Linux 8 container:
+
+```shell
+mage buildDockerEl8
+```
+
 For contributors who need a native build (Fedora / Rocky Linux 9), see
 [docs/build-rocky-linux-9.md](./docs/build-rocky-linux-9.md) and
 [AGENTS.md](./AGENTS.md).