Tracer scopes are used in numerous places in src/heap to track time
spent during various phases of the garbage collection. Usually, they
are introduced with the TRACE_GC* family of macros, taking the scope
identifier as a parameter. At most call sites, the scope identifier is
known at compile time.
This CL inlines the constructor and destructor of GCTracer::Scope, in
order to enable the C++ compiler to properly optimize the introduction
of such scopes when the scope identifier is known at compile time,
using constant propagation. This is expected to have a performance
impact for short-lived and frequently used scopes, e.g., in incremental
marking and sweeping steps.
Change-Id: I6f1a2954a437de1fa6dab5e464c20c952d84ffd4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3581774
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79957}
Method GCTracer::UpdateStatistics was responsible for copying
incremental and background scopes to the current event, before
reporting. It was called, however, at the end of the atomic pause and,
as a result, some of these scopes would be prematurely copied to the
current event (e.g., incremental and background sweeping scopes) and
misreported.
This CL fixes this by splitting the update of statistics and the
copying of incremental and background scopes. It introduces the
method GCTracer::FinalizeCurrentEvent which does the latter, which
is called from GCTracer::StopCycle. It also introduces methods for
correctly accessing and updating scopes, before the current event is
finalized, and eliminates the distinction between
GCTracer::AddScopeSample and GCTracer::AddScopeSampleBackground.
Bug: chromium:1154636
Change-Id: I2a6d9abb3daa2c48b2dce12dc2685cfc84130abf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3576792
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79938}
Similar to full GCs, the GC defers metric reporting until sweeping is
finished.
Bug: chromium:1029379
Change-Id: Ib06adb3be691c1ad2bd530eb77fc01cc22537338
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3576130
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Nikolaos Papaspyrou <nikolaos@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79891}
This CL moves the call to GCTracer::StopCycle for the full GC from
Heap::CompleteSweeping full, which is called to force sweeping to
finish, to GCTracer::NotifySweepingComplete, which is called as soon
as sweeping finishes --- and symmetrically to a new method
GCTracer::NotifyCppGCCompleted, which is called as soon as sweeping
of the managed C++ heap finishes. In this way, a full GC cycle is
reported as soon as sweeping is finished both for the V8 and the C++
managed heap.
The changes introduced in this CL are essentially a partial revert of
https://crrev.com/c/3456563, fixed in such a way that when the full
GC cycle is reported, the current tracer event will be the correct
one corresponding to that cycle.
Bug: v8:12503
Bug: chromium:1154636
Change-Id: Icea07cf35a9565994e798b0500e9da72cd95f9ac
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3497318
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79470}
The following histograms have been deprecated, as they are superseded
by V8.GC.Cycle.*.Young or not needed anymore (next to each, the
corresponding isolate counter):
- V8.GCScavenger (gc_scavenger)
- V8.GCScavengerBackground (gc_scavenger_background)
- V8.GCScavengeReason (scavenge_reason)
- V8.GCScavengerForeground (gc_scavenger_foreground)
- V8.GCBackgroundScavenger (background_scavenger)
- V8.GCMarkCompactor (gc_mark_compactor)
This CL removes the corresponding instrumentation in the code and the
isolate counters.
Bug: chromium:1154636
Bug: chromium:1299555
Change-Id: I62d28ff60ef47a058fe148c7855af8e2c1cc0aed
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3487548
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79308}
This CL refactors Heap::GCTypeTimer and Heap::GCTypePriorityTimer
and moves them to a GCTracer::RecordGCPhasesInfo class. This is
a necessary change for deprecating counters that are used for
old style GC metrics, like gc_scavenger. When all such counters
are deprecated, GCTracer::RecordGCPhasesInfo will no longer be
necessary and will be removed.
Bug: chromium:1154636
Change-Id: I04504a0f6c7a0955f4300a1c94c969aaeb23b77f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3486556
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79257}
This CL simplifies the reporting of full GC cycles and the connection
between the GC of the managed C++ heap and the managed Javascript heap.
It moves the call to GCTracer::RecordFullCycleToRecorder to be part of
GCTracer::StopCycle.
Bug: v8:12503
Bug: chromium:1154636
Change-Id: I332dbcd81d2e5bdda83f3353c6526fc18e23ebd5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3456563
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79075}
This CL fixes a bug in the tracing of full GC cycles that was introduced
by https://crrev.com/3432211. In doing so, it refactors the tracing of
cycles by introducing an explicit state in GC tracing events, which
follows the phase within the GC cycle as perceived by the tracer. Two
new methods, (Start|Stop)AtomicPause are introduced; together with
(Start|Stop)Cycle they mark the state transitions. The existing methods
(Start|Stop)ObservablePause are now disentangled from cycles and state
transitions.
Bug: v8:12503
Bug: chromium:1154636
Change-Id: Ie4b863bc27f81dd6858103a8988874d89e6e8517
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3440663
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79043}
Conceptually, a full GC cycle completes when the sweeping phase is
finished. As sweeping is performed concurrently, this happens after
Heap::CollectGarbage has returned and, at the latest, before the next
full GC cycle begins. However, an arbitrary number of young GC cycles
may happen in the meantime. Tracing information for the sweeping phase
must be added to the corresponding full GC cycle event. Until now, this
was not done correctly: this information was added to the GCTracer's
current event and could thus be attributed to a subsequent young or full
GC cycle.
This CL introduces methods GCTracer::(Start|Stop)Cycle to delimit a
cycle (still allowing for full GC cycles to be interrupted by young GC
cycles). These methods are different from (Start|Stop)ObservablePause,
which delimit the observable pause of each GC. The events of "pending"
full GC cycles are kept until they are properly amended and reported,
when the sweeping phase is finished.
This is a reland of 4ad20bff97
which was reviewed here: https://crrev.com/3404733
Bug: v8:12503
Bug: chromium:1154636
Change-Id: Icc315b53cff1f3b19b8efe49db34340a5608bcd2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3432211
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78911}
This reverts commit 4ad20bff97.
Reason for revert: New test seems to be failing on TSAN/incremental marking stress (https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20stress-incremental-marking/6346/overview)
Original change's description:
> heap: Fix the tracing of GC cycles
>
> Conceptually, a full GC cycle completes when the sweeping phase is
> finished. As sweeping is performed concurrently, this happens after
> Heap::CollectGarbage has returned and, at the latest, before the next
> full GC cycle begins. However, an arbitrary number of young GC cycles
> may happen in the meantime. Tracing information for the sweeping phase
> must be added to the corresponding full GC cycle event. Until now, this
> was not done correctly: this information was added to the GCTracer's
> current event and could thus be attributed to a subsequent young or full
> GC cycle.
>
> This CL introduces methods GCTracer::(Start|Stop)Cycle to delimit a
> cycle (still allowing for full GC cycles to be interrupted by young GC
> cycles). These methods are different from (Start|Stop)ObservablePause,
> which delimit the observable pause of each GC. The events of "pending"
> full GC cycles are kept until they are properly amended and reported,
> when the sweeping phase is finished.
>
> Bug: chromium:1154636
> Change-Id: I2fbc65d4807c78656d4abc8c451043f6f86211b1
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3404733
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78905}
Bug: chromium:1154636
Change-Id: Id6688cfe982f9d8159c66d715b7079782a371bed
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3431489
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78908}
Conceptually, a full GC cycle completes when the sweeping phase is
finished. As sweeping is performed concurrently, this happens after
Heap::CollectGarbage has returned and, at the latest, before the next
full GC cycle begins. However, an arbitrary number of young GC cycles
may happen in the meantime. Tracing information for the sweeping phase
must be added to the corresponding full GC cycle event. Until now, this
was not done correctly: this information was added to the GCTracer's
current event and could thus be attributed to a subsequent young or full
GC cycle.
This CL introduces methods GCTracer::(Start|Stop)Cycle to delimit a
cycle (still allowing for full GC cycles to be interrupted by young GC
cycles). These methods are different from (Start|Stop)ObservablePause,
which delimit the observable pause of each GC. The events of "pending"
full GC cycles are kept until they are properly amended and reported,
when the sweeping phase is finished.
Bug: chromium:1154636
Change-Id: I2fbc65d4807c78656d4abc8c451043f6f86211b1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3404733
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78905}
Remove TRACE_BACKGROUND_GC which was used to emit events on the
background thread. It is replaced by TRACE_GC1, which uses the ThreadKind
argument to work both on main and background threads.
This CL also removes the dedicated BackgroundScope enum, all scopes
are now in GCTracer::Scope.
Change-Id: Ie377082d6a278dd46f2fa359611fdd99a08afcea
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2560203
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71458}
Before this CL the main thread fetched the background GC stats and
added them to the main runtime-call-stats table. This resulted
in background GC stats showing up in the main thread trace.
This CL switches the background GC stats to use worker thread runtime-
calls-stats table. This is now consistent with other background
components of V8 suchs background compiler and parser.
Bug: v8:9508
Change-Id: Ic4c0685ded6024f78d0f22f81419fd5677202f25
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1776083
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63459}
This is a reland of a0728e869b
Original change's description:
> [d8] Remove maximum workers limitation
>
> This CL refactors the lifetime management of the v8::Worker C++ object
> and in the process lifts the 100 maximum worker limitation. To do this,
> it uses a Managed<v8::Worker> heap object and attaches the managed to
> the API worker object.
>
> R=mstarzinger@chromium.org
> BUG=v8:9524
>
> Change-Id: I279b7aeb6645a87f9108ee6f572105739721cef4
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1715453
> Commit-Queue: Ben Titzer <titzer@chromium.org>
> Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#62932}
Bug: v8:9524
Change-Id: I7d903fb12ddb00909a9429455f46c55db2fd02de
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1722562
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62974}
Provide a global memory controller used to compute limits for combined
on-heap and embedder memory. The global controller uses the same
mechanism (gc speed, mutator speed) and growing factors as the regular
on-heap controller.
Rely on V8's mechanisms for configured state that stops shrinking the
limit.
Reland:
- API fixes with overrides and default versions.
- Fix of depending on uninitialized values when using the old API.
- GCTracer: Fixed issue in speed computation.
- GCTracer: Added unittests.
This reverts commit 5e043f2773.
Bug: chromium:948807
Change-Id: I0f81253b3e1a8b49a7ac107c012a15e33cb514d7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622852
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61735}
This reverts commit dac86be251.
Reason for revert: Still failing msan: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/26904
Original change's description:
> Reland "[heap] Add global memory controller"
>
> Provide a global memory controller used to compute limits for combined
> on-heap and embedder memory. The global controller uses the same
> mechanism (gc speed, mutator speed) and growing factors as the regular
> on-heap controller.
>
> Rely on V8's mechanisms for configured state that stops shrinking the
> limit.
>
> This reverts commit 5e043f2773.
>
> Tbr: ulan@chromium.org
> Bug: chromium:948807
> Change-Id: Id4f94e7dcb458d1d0d2f872194f8f3ea0959a73f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622968
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61715}
TBR=ulan@chromium.org,mlippautz@chromium.org
Change-Id: If30649f158a08fd185f2771a13b8e09cf53fb667
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:948807
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622849
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61716}
Provide a global memory controller used to compute limits for combined
on-heap and embedder memory. The global controller uses the same
mechanism (gc speed, mutator speed) and growing factors as the regular
on-heap controller.
Rely on V8's mechanisms for configured state that stops shrinking the
limit.
This reverts commit 5e043f2773.
Tbr: ulan@chromium.org
Bug: chromium:948807
Change-Id: Id4f94e7dcb458d1d0d2f872194f8f3ea0959a73f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622968
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61715}
This reverts commit cfe281f3db.
Reason for revert: Fails on gcc bots
Original change's description:
> [heap] Add global memory controller
>
> Provide a global memory controller used to compute limits for combined
> on-heap and embedder memory. The global controller uses the same
> mechanism (gc speed, mutator speed) and growing factors as the regular
> on-heap controller.
>
> Rely on V8's mechanisms for configured state that stops shrinking the
> limit.
>
> Bug: chromium:948807
> Change-Id: I3283a2c28e6ab889f8d2ad85c9b67b8f234b9900
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1619762
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61712}
TBR=ulan@chromium.org,hpayer@chromium.org,mlippautz@chromium.org,bikineev@chromium.org
Change-Id: I503d5a1436eb9156556b5bca852d2b2f9da2446f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:948807
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622967
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61713}
Provide a global memory controller used to compute limits for combined
on-heap and embedder memory. The global controller uses the same
mechanism (gc speed, mutator speed) and growing factors as the regular
on-heap controller.
Rely on V8's mechanisms for configured state that stops shrinking the
limit.
Bug: chromium:948807
Change-Id: I3283a2c28e6ab889f8d2ad85c9b67b8f234b9900
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1619762
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61712}
Even though both are allowed in the style guide, it recommends to use
'using', as its syntax is more consistent with the rest of C++.
This CL turns all typedefs in heap code to 'using' declarations.
R=mstarzinger@chromium.org
Bug: v8:8834
Change-Id: I8a9f6e1eebdd0adca4373c866e95ebab0a1e992d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1545892
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60523}
The mock histogram functions cannot be cleared and can be called on
isolate tear down if incremental marking is in progress.
Bug: chromium:850508
Tbr: mlippautz@chromium.org
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I99e52aaa81c863f71e195aeed691b37da9e71da6
Reviewed-on: https://chromium-review.googlesource.com/1093073
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53616}
The mutator utilizaton is computed for each mark-compact GC cycle as
mutator_time / total_time, where
- total_time is the time from the end of the previous GC to the end of
the current GC
- mutator_time = total_time - incremental_steps_duration - gc_time.
Bug: chromium:824214
Change-Id: Ie1814f22f0816a3c9c579107f4950f6fc8c8a72d
Reviewed-on: https://chromium-review.googlesource.com/978215
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52221}
A background task can now use GCTracer::BackgroundScope to
trace the time spent in the task. The time shows up in
--trace-gc-nvp output and in the runtime call stats for GC.
The destructor of GCTracer::BackgroundScope increments the
corresponding counter in heap()->tracer()->background_counter_,
which is protected by a mutex.
The GCTracer::Stop function fetches background_counter_ items
into the global scope and into the runtime call stats.
Bug: chromium:758183
Change-Id: Id7bcd5089ba6c027fe9a57eb3f7db1cb5092aec5
Reviewed-on: https://chromium-review.googlesource.com/801694
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49841}
This patch replaces cumulative counters with the counters for the current GC cycle.
It also replaces the ring buffer of record incremental marking speeds with a single variable.
Review-Url: https://codereview.chromium.org/2361563004
Cr-Commit-Position: refs/heads/master@{#39826}
Now callers of Heap::CollectGarbage* functions need to
specify the reason as an enum value instead of a string.
Subsequent CL will add stats counter for GC reason.
BUG=
Review-Url: https://codereview.chromium.org/2310143002
Cr-Commit-Position: refs/heads/master@{#39239}
Record details, such as cumulative duration, number of steps, and longest steps
in IncrementalMarkingDetails which get populated at a single callsite
(AddScopeSample). Remove member fields that thus become obsolete (unfortunately
not all of them).
Additional remove some dead code and refactor printing. Printing in a single
statement allows for using logcat on Android.
This should also address the regression in chromium:640524.
BUG=chromium:639818,chromium:640524
R=jochen@chromium.org
Review-Url: https://codereview.chromium.org/2269093002
Cr-Commit-Position: refs/heads/master@{#38912}
Before this patch all tracing scopes in incremental marking would be reset
during a gc tracer start/stop cycle. This patch handles scopes the same way it
does other incremental marking metrics.
Also:
- Align finalization metric with regular marking metric.
- Smaller cleanups
BUG=chromium:639818
Review-Url: https://codereview.chromium.org/2273673002
Cr-Commit-Position: refs/heads/master@{#38834}
Before this patch all tracing scopes in incremental marking would be reset
during a gc tracer start/stop cycle. This patch handles scopes the same way it
does other incremental marking metrics.
Also:
- Align finalization metric with regular marking metric.
- Smaller cleanups
BUG=chromium:639818
R=jochen@chromium.org
Review-Url: https://codereview.chromium.org/2264033002
Cr-Commit-Position: refs/heads/master@{#38822}
This avoids redundant casts, loss of precision, and potential overflows.
BUG=chromium:597310
LOG=NO
Review URL: https://codereview.chromium.org/1841043002
Cr-Commit-Position: refs/heads/master@{#35113}
Now instead of saving all event details in the ring buffer,
we save only the bytes and duration.
This reduces the GCTracer size from 20K to 3K and simplifies code.
BUG=chromium:597310
LOG=NO
Review URL: https://codereview.chromium.org/1830723004
Cr-Commit-Position: refs/heads/master@{#35104}
