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| //===--------------------- TimelineView.h -----------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \brief
///
/// This file implements a timeline view for the llvm-mca tool.
///
/// Class TimelineView observes events generated by the pipeline. For every
/// instruction executed by the pipeline, it stores information related to
/// state transition. It then plots that information in the form of a table
/// as reported by the example below:
///
/// Timeline view:
/// 0123456
/// Index 0123456789
///
/// [0,0] DeER . . .. vmovshdup %xmm0, %xmm1
/// [0,1] DeER . . .. vpermilpd $1, %xmm0, %xmm2
/// [0,2] .DeER. . .. vpermilps $231, %xmm0, %xmm5
/// [0,3] .DeeeER . .. vaddss %xmm1, %xmm0, %xmm3
/// [0,4] . D==eeeER. .. vaddss %xmm3, %xmm2, %xmm4
/// [0,5] . D=====eeeER .. vaddss %xmm4, %xmm5, %xmm6
///
/// [1,0] . DeE------R .. vmovshdup %xmm0, %xmm1
/// [1,1] . DeE------R .. vpermilpd $1, %xmm0, %xmm2
/// [1,2] . DeE-----R .. vpermilps $231, %xmm0, %xmm5
/// [1,3] . D=eeeE--R .. vaddss %xmm1, %xmm0, %xmm3
/// [1,4] . D===eeeER .. vaddss %xmm3, %xmm2, %xmm4
/// [1,5] . D======eeeER vaddss %xmm4, %xmm5, %xmm6
///
/// There is an entry for every instruction in the input assembly sequence.
/// The first field is a pair of numbers obtained from the instruction index.
/// The first element of the pair is the iteration index, while the second
/// element of the pair is a sequence number (i.e. a position in the assembly
/// sequence).
/// The second field of the table is the actual timeline information; each
/// column is the information related to a specific cycle of execution.
/// The timeline of an instruction is described by a sequence of character
/// where each character represents the instruction state at a specific cycle.
///
/// Possible instruction states are:
/// D: Instruction Dispatched
/// e: Instruction Executing
/// E: Instruction Executed (write-back stage)
/// R: Instruction retired
/// =: Instruction waiting in the Scheduler's queue
/// -: Instruction executed, waiting to retire in order.
///
/// dots ('.') and empty spaces are cycles where the instruction is not
/// in-flight.
///
/// The last column is the assembly instruction associated to the entry.
///
/// Based on the timeline view information from the example, instruction 0
/// at iteration 0 was dispatched at cycle 0, and was retired at cycle 3.
/// Instruction [0,1] was also dispatched at cycle 0, and it retired at
/// the same cycle than instruction [0,0].
/// Instruction [0,4] has been dispatched at cycle 2. However, it had to
/// wait for two cycles before being issued. That is because operands
/// became ready only at cycle 5.
///
/// This view helps further understanding bottlenecks and the impact of
/// resource pressure on the code.
///
/// To better understand why instructions had to wait for multiple cycles in
/// the scheduler's queue, class TimelineView also reports extra timing info
/// in another table named "Average Wait times" (see example below).
///
///
/// Average Wait times (based on the timeline view):
/// [0]: Executions
/// [1]: Average time spent waiting in a scheduler's queue
/// [2]: Average time spent waiting in a scheduler's queue while ready
/// [3]: Average time elapsed from WB until retire stage
///
/// [0] [1] [2] [3]
/// 0. 2 1.0 1.0 3.0 vmovshdup %xmm0, %xmm1
/// 1. 2 1.0 1.0 3.0 vpermilpd $1, %xmm0, %xmm2
/// 2. 2 1.0 1.0 2.5 vpermilps $231, %xmm0, %xmm5
/// 3. 2 1.5 0.5 1.0 vaddss %xmm1, %xmm0, %xmm3
/// 4. 2 3.5 0.0 0.0 vaddss %xmm3, %xmm2, %xmm4
/// 5. 2 6.5 0.0 0.0 vaddss %xmm4, %xmm5, %xmm6
/// 2 2.4 0.6 1.6 <total>
///
/// By comparing column [2] with column [1], we get an idea about how many
/// cycles were spent in the scheduler's queue due to data dependencies.
///
/// In this example, instruction 5 spent an average of ~6 cycles in the
/// scheduler's queue. As soon as operands became ready, the instruction
/// was immediately issued to the pipeline(s).
/// That is expected because instruction 5 cannot transition to the "ready"
/// state until %xmm4 is written by instruction 4.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_TOOLS_LLVM_MCA_TIMELINEVIEW_H
#define LLVM_TOOLS_LLVM_MCA_TIMELINEVIEW_H
#include "Views/View.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstPrinter.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/raw_ostream.h"
namespace llvm {
namespace mca {
/// This class listens to instruction state transition events
/// in order to construct a timeline information.
///
/// For every instruction executed by the Pipeline, this class constructs
/// a TimelineViewEntry object. TimelineViewEntry objects are then used
/// to print the timeline information, as well as the "average wait times"
/// for every instruction in the input assembly sequence.
class TimelineView : public View {
const llvm::MCSubtargetInfo &STI;
llvm::MCInstPrinter &MCIP;
llvm::ArrayRef<llvm::MCInst> Source;
unsigned CurrentCycle;
unsigned MaxCycle;
unsigned LastCycle;
struct TimelineViewEntry {
int CycleDispatched; // A negative value is an "invalid cycle".
unsigned CycleReady;
unsigned CycleIssued;
unsigned CycleExecuted;
unsigned CycleRetired;
};
std::vector<TimelineViewEntry> Timeline;
struct WaitTimeEntry {
unsigned CyclesSpentInSchedulerQueue;
unsigned CyclesSpentInSQWhileReady;
unsigned CyclesSpentAfterWBAndBeforeRetire;
};
std::vector<WaitTimeEntry> WaitTime;
// This field is used to map instructions to buffered resources.
// Elements of this vector are <resourceID, BufferSizer> pairs.
std::vector<std::pair<unsigned, int>> UsedBuffer;
void printTimelineViewEntry(llvm::formatted_raw_ostream &OS,
const TimelineViewEntry &E, unsigned Iteration,
unsigned SourceIndex) const;
void printWaitTimeEntry(llvm::formatted_raw_ostream &OS,
const WaitTimeEntry &E, unsigned Index,
unsigned Executions) const;
// Display characters for the TimelineView report output.
struct DisplayChar {
static const char Dispatched = 'D';
static const char Executed = 'E';
static const char Retired = 'R';
static const char Waiting = '='; // Instruction is waiting in the scheduler.
static const char Executing = 'e';
static const char RetireLag = '-'; // The instruction is waiting to retire.
};
public:
TimelineView(const llvm::MCSubtargetInfo &sti, llvm::MCInstPrinter &Printer,
llvm::ArrayRef<llvm::MCInst> S, unsigned Iterations,
unsigned Cycles);
// Event handlers.
void onCycleEnd() override { ++CurrentCycle; }
void onEvent(const HWInstructionEvent &Event) override;
void onReservedBuffers(const InstRef &IR,
llvm::ArrayRef<unsigned> Buffers) override;
// print functionalities.
void printTimeline(llvm::raw_ostream &OS) const;
void printAverageWaitTimes(llvm::raw_ostream &OS) const;
void printView(llvm::raw_ostream &OS) const override {
printTimeline(OS);
printAverageWaitTimes(OS);
}
};
} // namespace mca
} // namespace llvm
#endif
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