This is an automated email from the git hooks/post-receive script. x2go pushed a commit to branch upstream/28.4.0 in repository pale-moon. commit b55d41c240df13812760a2a77f086a477f450fd0 Author: David Teller <dteller@mozilla.com> Date: Tue Jan 29 03:11:39 2019 +0100 Reduce number of allocations in AutoStopwatch This patch fixes two related issues. 1. The AutoStopwatch uses a stack-allocated `mozilla::Vector` to communicate with its callback during each compartment switch. This vector was designed to allow its contents to be stack-allocated but they turned out to be accidentally heap-allocated. 2. During each tick, the stopwatch fills a vector `recentGroups_`. This vector always started with minimal capacity and had to grow repeatedly as groups were added, causing repeated reallocations. This patch preallocates `recentGroups_` to have the same capacity as the previous tick. We expect that this should eventually reach a stable size that closely matches the actual needs of the process. --- js/src/jsapi.h | 2 +- js/src/vm/Stopwatch.cpp | 25 +++++++++++++++++----- .../perfmonitoring/nsPerformanceStats.cpp | 11 ++++++++-- .../components/perfmonitoring/nsPerformanceStats.h | 2 +- 4 files changed, 31 insertions(+), 9 deletions(-) diff --git a/js/src/jsapi.h b/js/src/jsapi.h index 0983f03..799396a 100644 --- a/js/src/jsapi.h +++ b/js/src/jsapi.h @@ -6566,7 +6566,7 @@ struct JS_PUBLIC_API(PerformanceGroup) { uint64_t refCount_; }; -using PerformanceGroupVector = mozilla::Vector<RefPtr<js::PerformanceGroup>, 0, SystemAllocPolicy>; +using PerformanceGroupVector = mozilla::Vector<RefPtr<js::PerformanceGroup>, 8, SystemAllocPolicy>; /** * Commit any Performance Monitoring data. diff --git a/js/src/vm/Stopwatch.cpp b/js/src/vm/Stopwatch.cpp index 7a6acb9..5b5ec61 100644 --- a/js/src/vm/Stopwatch.cpp +++ b/js/src/vm/Stopwatch.cpp @@ -20,6 +20,7 @@ #include "gc/Zone.h" #include "vm/Runtime.h" + namespace js { bool @@ -136,6 +137,9 @@ PerformanceMonitoring::start() bool PerformanceMonitoring::commit() { + // Maximal initialization size, in elements for the vector of groups. + static const size_t MAX_GROUPS_INIT_CAPACITY = 1024; + #if !defined(MOZ_HAVE_RDTSC) // The AutoStopwatch is only executed if `MOZ_HAVE_RDTSC`. return false; @@ -152,13 +156,24 @@ PerformanceMonitoring::commit() return true; } - PerformanceGroupVector recentGroups; - recentGroups_.swap(recentGroups); + // The move operation is generally constant time, unless + // `recentGroups_.length()` is very small, in which case + // it's fast just because it's small. + PerformanceGroupVector recentGroups(Move(recentGroups_)); + recentGroups_ = PerformanceGroupVector(); // Reconstruct after `Move`. bool success = true; if (stopwatchCommitCallback) success = stopwatchCommitCallback(iteration_, recentGroups, stopwatchCommitClosure); + // Heuristic: we expect to have roughly the same number of groups as in + // the previous iteration. + const size_t capacity = recentGroups.capacity() < MAX_GROUPS_INIT_CAPACITY ? + recentGroups.capacity() : + MAX_GROUPS_INIT_CAPACITY; + success = recentGroups_.reserve(capacity) + && success; + // Reset immediately, to make sure that we're not hit by the end // of a nested event loop (which would cause `commit` to be called // twice in succession). @@ -227,7 +242,7 @@ AutoStopwatch::AutoStopwatch(JSContext* cx MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IM MOZ_GUARD_OBJECT_NOTIFIER_INIT; JSCompartment* compartment = cx_->compartment(); - if (compartment->scheduledForDestruction) + if (MOZ_UNLIKELY(compartment->scheduledForDestruction)) return; JSRuntime* runtime = cx_->runtime(); @@ -266,11 +281,11 @@ AutoStopwatch::~AutoStopwatch() } JSCompartment* compartment = cx_->compartment(); - if (compartment->scheduledForDestruction) + if (MOZ_UNLIKELY(compartment->scheduledForDestruction)) return; JSRuntime* runtime = cx_->runtime(); - if (iteration_ != runtime->performanceMonitoring.iteration()) { + if (MOZ_UNLIKELY(iteration_ != runtime->performanceMonitoring.iteration())) { // We have entered a nested event loop at some point. // Any information we may have is obsolete. return; diff --git a/toolkit/components/perfmonitoring/nsPerformanceStats.cpp b/toolkit/components/perfmonitoring/nsPerformanceStats.cpp index 6c47035..59d84ce 100644 --- a/toolkit/components/perfmonitoring/nsPerformanceStats.cpp +++ b/toolkit/components/perfmonitoring/nsPerformanceStats.cpp @@ -1082,6 +1082,9 @@ nsPerformanceStatsService::GetPerformanceGroups(JSContext* cx, return false; } + // Returning a vector that is too large would cause allocations all over the + // place in the JS engine. We want to be sure that all data is stored inline. + MOZ_ASSERT(out.length() <= out.sMaxInlineStorage); return true; } @@ -1310,8 +1313,12 @@ nsPerformanceStatsService::GetResources(uint64_t* userTime, void nsPerformanceStatsService::NotifyJankObservers(const mozilla::Vector<uint64_t>& aPreviousJankLevels) { - GroupVector alerts; - mPendingAlerts.swap(alerts); + + // The move operation is generally constant time, unless + // `mPendingAlerts.length()` is very small, in which case it's fast anyway. + GroupVector alerts(Move(mPendingAlerts)); + mPendingAlerts = GroupVector(); // Reconstruct after `Move`. + if (!mPendingAlertsCollector) { // We are shutting down. return; diff --git a/toolkit/components/perfmonitoring/nsPerformanceStats.h b/toolkit/components/perfmonitoring/nsPerformanceStats.h index 6902c84..661a78a 100644 --- a/toolkit/components/perfmonitoring/nsPerformanceStats.h +++ b/toolkit/components/perfmonitoring/nsPerformanceStats.h @@ -19,7 +19,7 @@ class nsPerformanceGroup; class nsPerformanceGroupDetails; -typedef mozilla::Vector<RefPtr<nsPerformanceGroup>> GroupVector; +typedef mozilla::Vector<RefPtr<nsPerformanceGroup>, 8> GroupVector; /** * A data structure for registering observers interested in -- Alioth's /home/x2go-admin/maintenancescripts/git/hooks/post-receive-email on /srv/git/code.x2go.org/pale-moon.git