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Serve KVM's binary statistics (KVM_GET_STATS_FD, Linux 5.14+) for the VM and each vCPU. Each statistic carries the kind and unit KVM declares for it, named as in QEMU's query-stats, and histograms such as halt_wait_hist are returned in full: debugfs only has per-VM sums and reads histograms as their first bucket. The stats descriptors are opened when the vCPUs are created, before the VMM thread's seccomp filter is installed, and read with pread64 on each request, which the VMM filter now allows. Values are running totals since the vCPUs were created, so they start from zero after a snapshot is loaded. Signed-off-by: Lisa Goh <[email protected]>
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Closes #6288
Changes
Serve KVM's binary statistics (KVM_GET_STATS_FD, Linux 5.14+) for the VM and each vCPU. Each statistic carries the kind and unit KVM declares for it, named as in QEMU's query-stats, and histograms such as halt_wait_hist are returned in full: debugfs only has per-VM sums and reads histograms as their first bucket.
The stats descriptors are opened when the vCPUs are created, before the VMM thread's seccomp filter is installed, and read with pread64 on each request, which the VMM filter now allows. Values are running totals since the vCPUs were created, so they start from zero after a snapshot is loaded.
Reason
When a VM is slow, we want to know where its vCPUs spent their time: running guest code, exiting to KVM, halted, or halt-polling. KVM counts this per vCPU and, since Linux 5.14, exposes it through binary stats (KVM_GET_STATS_FD), including histograms such as halt_wait_hist. Firecracker's metrics only cover the exits that reach Firecracker itself (vcpu.exit_mmio_, vcpu.exit_io_).
License Acceptance
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CONTRIBUTING.md.PR Checklist
tools/devtool checkbuild --allto verify that the PR passesbuild checks on all supported architectures.
tools/devtool checkstyle --no-clippyto verify that the PRpasses the automated style checks.
how they are solving the problem in a clear and encompassing way.
in the PR.
CHANGELOG.md.Runbook for Firecracker API changes.
integration tests.
TODO.rust-vmm.