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authorAyush Ranjan <ayushranjan@google.com>2021-04-16 18:44:43 -0700
committergVisor bot <gvisor-bot@google.com>2021-04-16 18:47:08 -0700
commit3b685753b4e9632ed8cde1ae284c79a9a14230b9 (patch)
tree014c090423c6fb3d75c2019421ec7177d5f9ef7e /pkg/sentry/usage/usage.go
parent0c3e8daf503e011f0ef3e2a1c6d8b6ffd946acab (diff)
[perf] Reduce contention due to renameMu in gofer client.
Runsc build benchmark's mutex profile shows that we are wasting roughly 25-30 seconds waiting for filesystem.renameMu to get unlocked. Earlier checkCachingLocked required the renameMu to be locked for writing. This is a filesystem wide lock which puts all other filesystem operations on hold and hence is really expensive. Something to note is that all path resolution operations hold renameMu for reading. With this change, we allow to check for caching without even holding renameMu. This change introduces more fine grained locks (fs.cacheMu and dentry.cachingMu) which protect the cache (removing the requirement to hold renameMu for writing to modify the cache) and synchronize concurrent dentry caching attempts on a per dentry basis. We still require to hold renameMu for writing while destroying dentries and evicting from the cache but this still significantly reduces the write locking critical section. Local benchmarking showed that this improved runsc build benchmark time by 4-5%. Across 6 runs, without this change it took 310.9025 seconds to build runsc while with this change it took 296.127 seconds. Runsc build benchmark's mutex profile: https://gvisor.dev/profile/gvisor-buildkite/78a3f968-36ca-4944-93f7-77a8792d56b4/28a1d260-790b-4a9e-94da-a4daede08ee3/tmp/profile/ptrace/BenchmarkBuildRunsc/page_cache.clean/filesystem.bindfs/benchmarks/runsc/mutex.pprof/flamegraph PiperOrigin-RevId: 368958136
Diffstat (limited to 'pkg/sentry/usage/usage.go')
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