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lyphyserandHanzo Dev
26b6f703f1
The deepSleepTimeout/handshakeTimeout thresholds bound how long stub threads and the dispatcher spin before deep-sleeping. They were hardcoded in cputicks() units tuned for the amd64 TSC (~2GHz), e.g. 40000 ticks for "20µs". But cputicks() advances at a platform-specific rate unrelated to the CPU clock: on arm64 it reads CNTVCT_EL0, which runs at CNTFRQ_EL0 -- anywhere from tens of MHz up to ~1GHz depending on the core -- so a fixed tick count maps to a different wall-clock duration there. On a tens-of-MHz part, 40000 ticks is ~2ms (~100x the intended 20µs), so idle stub threads and the dispatcher spin far too long before sleeping, burning CPU on otherwise idle containers (issue #13361). Neither RDTSC nor CNTVCT_EL0 is an instruction/cycle counter; both are constant-rate time references at frequencies that differ per platform, so the timeouts are fundamentally durations. Express them once as nanosecond durations and convert to cputicks() units via a new per-arch cputicksFreq(): - arm64 reads CNTFRQ_EL0 (exact, no calibration). - amd64 returns the nominal 2GHz the constants were tuned against, so amd64 behavior is unchanged. initSleepTimeouts() performs the conversion once in New(), before stubInit() copies deepSleepTimeout into the stub. Co-authored-by: Hanzo Dev <[email protected]>
60 lines
2.3 KiB
Go
60 lines
2.3 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package systrap
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import (
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/sentry/arch"
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)
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// getCNTFRQ returns the frequency (in Hz) of the system counter read by
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// cputicks(), as reported by CNTFRQ_EL0.
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func getCNTFRQ() int64
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// typicalCNTFRQ is a fallback system counter frequency (24MHz, a common
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// reference-crystal value) used only if CNTFRQ_EL0 reads back as zero. The
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// architecture requires firmware to program CNTFRQ_EL0, so real hardware always
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// reports a non-zero value; this only guards against a misconfigured board.
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// Actual frequencies vary widely -- from tens of MHz up to ~1GHz on newer
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// cores -- so this is a best-effort guess, not a value that fits all hardware.
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const typicalCNTFRQ = 24 * 1000 * 1000
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// cputicksFreq returns the frequency in Hz of the counter read by cputicks().
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// On arm64 cputicks() reads CNTVCT_EL0, whose frequency is reported exactly by
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// CNTFRQ_EL0, so no calibration is needed. It always returns a non-zero value:
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// the sleep-timeout conversion needs a frequency, and there is no sane
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// cross-platform default (the counter rate is platform-specific and ranges from
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// tens of MHz to ~GHz), so the fallback must be arch-specific.
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func cputicksFreq() uint64 {
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if freq := getCNTFRQ(); freq > 0 {
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return uint64(freq)
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}
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return typicalCNTFRQ
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}
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func stackPointer(r *arch.Registers) uintptr {
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return uintptr(r.Sp)
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}
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// configureSystrapAddressSpace overrides the default 48-bit address space
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// parameters when the host uses a different VA width. On 48-bit VA hosts,
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// ConfigureAddressSpace(1<<48) re-affirms the defaults.
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//
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// This function MUST be called during systrap initialization, before any
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// Context64 is created.
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func configureSystrapAddressSpace() {
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arch.ConfigureAddressSpace(uintptr(linux.TaskSize))
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}
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