The last remaining !go1.22 build is protecting the definition of
pkg/sync.maptype, which is a copy of runtime.maptype. We need to ensure these
definitions match so we can safely access the hasher field.
At its core, this CL achieves this check by ensuring that
unsafe.Offsetof(maptype{}.Hasher) matches the offset in the runtime version of
the type.
Several things happen along the way to achieve this:
* As of May 2023, runtime.maptype is actually a type alias for
internal/abi.MapType. checkoffset was failing to record the offsets because it
skipped type aliases for no good reason. Simply removing the type alias check
is sufficient to make type aliases work. (This part of the CL is technically
unnecessary because this CL ultimately references internal/abi.MapType
directly in anticipation of removal of the type alias. But there is no reason
not to allow type aliases).
* The checkconst / checkoffset regexp unintentionally does not allow / in
package paths, even though the rest of the package supports /. Fix this.
* checkconst was comparing the literal AST expression string against the
runtime value (i.e., "unsafe.Offsetof(maptype{}.Hasher)" vs "72", which fails
comparison. Switch to getting the resolved constant value from the type
checker.
* nogo/check.importer only loads package facts on direct import (stored in
importer.cache). If a package is not directly imported ImportPackageFact will
not find the facts. Typically packages need to ensure they directly depend on
packages they want facts from (e.g., pkg/sync has a dummy import of runtime in
runtime.go). This doesn't work for internal/abi because we cannot directly
import an internal package. Work around this as a hack by unconditionally
"importing" internal/abi when analyzing any package.
With regard to the last point, not that the nogo/defs.bzl nogo integration only
provides facts from the direct dependencies and the entire stdlib (since the
stdlib is analyzed as one bundle). So this trick only works for a stdlib
package. A bazel package indirect dependency would be missing facts altogether.
PiperOrigin-RevId: 549999084
cl/504661697 removes this build tag once and for all, but it is blocked on
additional work needed to get it working with OSS bazel builds.
Until that is ready, bump the build tag to unblock testing Go tip (1.21).
PiperOrigin-RevId: 505923005
Upstream Go tip has updated its version to 1.19, so we need to bump these build
tags to allow tip testing.
This CL bumps the minimum version in pkg/sync/runtime_amd64.s from 1.8 to 1.14.
The offset was different prior to Go 1.14.
Ideally we'll get checklinkname (or equivalent) to check these remaining unsafe
uses (like internal struct field offsets) soon.
For golang/go#51445.
PiperOrigin-RevId: 433304124
The fdnotifier goroutine alternates between [host] epoll_wait()ing for I/O
readiness events and propagating those events through the sentry, possibly
waking task goroutines blocked in e.g. [application] epoll_wait(). Since woken
goroutines are queued on the runqueue of the waking P (cf. runtime.ready()),
these goroutines will almost always wait to execute until another OS thread
takes them (either directly via runtime.runqsteal(), or indirectly via sysmon
stealing the P and runtime.handoffp()ing it to another thread). Furthermore,
epoll_wait() is most likely to block (new events are least likely to have
arrived) shortly after a previous call (on the same epoll FD) returns events,
so this behavior utilizes the thread's OS-scheduled time slice poorly. Avoid
both of these problems by runtime.goyield()ing between goroutine wakeup and
epoll_wait().
PiperOrigin-RevId: 430793631
Some synchronization patterns require the ability to simultaneously wake and
sleep a goroutine. For the sleep package, this is the case when a waker must be
asserted when a subsequent fetch is imminent.
Currently, this operation results in significant P churn in the runtime, which
ping-pongs execution between multiple system threads and cores and consumes a
significant amount of host CPU (and because of the context switches, this can
be significant worse with mitigations for side channel vulnerabilities).
The solution is to introduce a dedicated mechanism for a synchronous switch
which does not wake another runtime P (see golang/go#32113). This can be used
by the `AssertAndFetch` API in the sleep package.
The benchmark results for this package are very similiar to raw channel
operations for all cases, with the exception of operations that do not wait.
The primary advantage is more precise control over scheduling. This will be
used in a subsequent change.
```
BenchmarkGoAssertNonWaiting
BenchmarkGoAssertNonWaiting-8 261364384 4.976 ns/op
BenchmarkGoSingleSelect
BenchmarkGoSingleSelect-8 20946358 57.77 ns/op
BenchmarkGoMultiSelect
BenchmarkGoMultiSelect-8 6071697 197.0 ns/op
BenchmarkGoWaitOnSingleSelect
BenchmarkGoWaitOnSingleSelect-8 4978051 235.4 ns/op
BenchmarkGoWaitOnMultiSelect
BenchmarkGoWaitOnMultiSelect-8 2309224 520.2 ns/op
BenchmarkSleeperAssertNonWaiting
BenchmarkSleeperAssertNonWaiting-8 447325033 2.657 ns/op
BenchmarkSleeperSingleSelect
BenchmarkSleeperSingleSelect-8 21488844 55.19 ns/op
BenchmarkSleeperMultiSelect
BenchmarkSleeperMultiSelect-8 21851674 54.89 ns/op
BenchmarkSleeperWaitOnSingleSelect
BenchmarkSleeperWaitOnSingleSelect-8 2860327 416.4 ns/op
BenchmarkSleeperWaitOnSingleSelectSync
BenchmarkSleeperWaitOnSingleSelectSync-8 2741733 427.1 ns/op
BenchmarkSleeperWaitOnMultiSelect
BenchmarkSleeperWaitOnMultiSelect-8 2867484 418.1 ns/op
BenchmarkSleeperWaitOnMultiSelectSync
BenchmarkSleeperWaitOnMultiSelectSync-8 2789158 427.9 ns/op
```
PiperOrigin-RevId: 415581417
Go's dev.typeparams branch already claims to be Go 1.18, so our !go1.18 build
tags breaking testing gVisor with that branch.
Normally I would not want to bump the build tags this early, but I plan to
extend checklinkname to check the assumptions in these files and remove the
build tags ASAP. So we just go ahead and bump the tags until then to unblock
testing.
PiperOrigin-RevId: 389037239
This CL introduces a 'checklinkname' analyzer, which provides rudimentary
type-checking that verifies that function signatures on the local and remote
sides of //go:linkname directives match expected values.
If the Go standard library changes the definitions of any of these function,
checklinkname will flag the change as a finding, providing an error informing
the gVisor team to adapt to the upstream changes. This allows us to eliminate
the majority of gVisor's forward-looking negative build tags, as we can catch
mismatches in testing [1].
The remaining forward-looking negative build tags are covering shared struct
definitions, which I hope to add to checklinkname in a future CL.
[1] Of course, semantics/requirements can change without the signature
changing, so we still must be careful, but this covers the common case.
PiperOrigin-RevId: 387873847
- Use atomic add rather than CAS in every Gate method, which is slightly
faster in most cases.
- Implement Close wakeup using gopark/goready to avoid channel allocation.
New benchmarks:
name old time/op new time/op delta
GateEnterLeave-12 16.7ns ± 1% 10.3ns ± 1% -38.44% (p=0.000 n=9+8)
GateClose-12 50.2ns ± 8% 42.4ns ± 6% -15.44% (p=0.000 n=10+10)
GateEnterLeaveAsyncClose-12 972ns ± 2% 640ns ± 7% -34.15% (p=0.000 n=9+10)
PiperOrigin-RevId: 359336344
