lesson_21_auto_scheduler_generate.cpp
// Halide tutorial lesson 21: Auto-Scheduler
// So far we have written Halide schedules by hand, but it is also possible to
// ask Halide to suggest a reasonable schedule. We call this auto-scheduling.
// This lesson demonstrates how to use the auto-scheduler to generate a
// copy-pasteable CPU schedule that can be subsequently improved upon.
// On linux or os x, you can compile and run it like so:
// g++ lesson_21_auto_scheduler_generate.cpp ../tools/GenGen.cpp -g -std=c++11 -fno-rtti -I ../include -L ../bin -lHalide -lpthread -ldl -o lesson_21_generate
// export LD_LIBRARY_PATH=../bin # For linux
// export DYLD_LIBRARY_PATH=../bin # For OS X
// ./lesson_21_generate -o . -g auto_schedule_gen -f auto_schedule_false -e static_library,h,schedule target=host auto_schedule=false
// ./lesson_21_generate -o . -g auto_schedule_gen -f auto_schedule_true -e static_library,h,schedule target=host auto_schedule=true machine_params=32,16777216,40
// g++ lesson_21_auto_scheduler_run.cpp -std=c++11 -I ../include -I ../tools auto_schedule_false.a auto_schedule_true.a -ldl -lpthread -o lesson_21_run
// ./lesson_21_run
// If you have the entire Halide source tree, you can also build it by
// running:
// make tutorial_lesson_21_auto_scheduler_run
// in a shell with the current directory at the top of the halide
// source tree.
#include "Halide.h"
#include <stdio.h>
using namespace Halide;
// We will define a generator to auto-schedule.
class AutoScheduled : public Halide::Generator<AutoScheduled> {
public:
Input<Buffer<float>> input{"input", 3};
Input<float> factor{"factor"};
Output<Buffer<float>> output1{"output1", 2};
Output<Buffer<float>> output2{"output2", 2};
Expr sum3x3(Func f, Var x, Var y) {
return f(x - 1, y - 1) + f(x - 1, y) + f(x - 1, y + 1) +
f(x, y - 1) + f(x, y) + f(x, y + 1) +
f(x + 1, y - 1) + f(x + 1, y) + f(x + 1, y + 1);
}
void generate() {
// For our algorithm, we'll use Harris corner detection.
Func in_b = BoundaryConditions::repeat_edge(input);
gray(x, y) = 0.299f * in_b(x, y, 0) + 0.587f * in_b(x, y, 1) + 0.114f * in_b(x, y, 2);
Iy(x, y) = gray(x - 1, y - 1) * (-1.0f / 12) + gray(x - 1, y + 1) * (1.0f / 12) +
gray(x, y - 1) * (-2.0f / 12) + gray(x, y + 1) * (2.0f / 12) +
gray(x + 1, y - 1) * (-1.0f / 12) + gray(x + 1, y + 1) * (1.0f / 12);
Ix(x, y) = gray(x - 1, y - 1) * (-1.0f / 12) + gray(x + 1, y - 1) * (1.0f / 12) +
gray(x - 1, y) * (-2.0f / 12) + gray(x + 1, y) * (2.0f / 12) +
gray(x - 1, y + 1) * (-1.0f / 12) + gray(x + 1, y + 1) * (1.0f / 12);
Ixx(x, y) = Ix(x, y) * Ix(x, y);
Iyy(x, y) = Iy(x, y) * Iy(x, y);
Ixy(x, y) = Ix(x, y) * Iy(x, y);
Sxx(x, y) = sum3x3(Ixx, x, y);
Syy(x, y) = sum3x3(Iyy, x, y);
Sxy(x, y) = sum3x3(Ixy, x, y);
det(x, y) = Sxx(x, y) * Syy(x, y) - Sxy(x, y) * Sxy(x, y);
trace(x, y) = Sxx(x, y) + Syy(x, y);
harris(x, y) = det(x, y) - 0.04f * trace(x, y) * trace(x, y);
output1(x, y) = harris(x + 2, y + 2);
output2(x, y) = factor * harris(x + 2, y + 2);
}
void schedule() {
if (auto_schedule) {
// The auto-scheduler requires estimates on all the input/output
// sizes and parameter values in order to compare different
// alternatives and decide on a good schedule.
// To provide estimates (min and extent values) for each dimension
// of the input images ('input', 'filter', and 'bias'), we use the
// set_estimates() method. set_estimates() takes in a list of
// (min, extent) of the corresponding dimension as arguments.
input.set_estimates({{0, 1024}, {0, 1024}, {0, 3}});
// To provide estimates on the parameter values, we use the
// set_estimate() method.
factor.set_estimate(2.0f);
// To provide estimates (min and extent values) for each dimension
// of pipeline outputs, we use the set_estimates() method. set_estimates()
// takes in a list of (min, extent) for each dimension.
output1.set_estimates({{0, 1024}, {0, 1024}});
output2.set_estimates({{0, 1024}, {0, 1024}});
// Technically, the estimate values can be anything, but the closer
// they are to the actual use-case values, the better the generated
// schedule will be.
// To auto-schedule the the pipeline, we don't have to do anything else:
// every Generator implicitly has a GeneratorParam named "auto_schedule";
// if this is set to true, Halide will call auto_schedule() on all of
// our pipeline's outputs automatically.
// Every Generator also implicitly has a GeneratorParams named "machine_params",
// which allows you to specify characteristics of the machine architecture
// for the auto-scheduler; it's generally specified in your Makefile.
// If none is specified, the default machine parameters for a generic CPU
// architecture will be used by the auto-scheduler.
// Let's see some arbitrary but plausible values for the machine parameters.
//
// const int kParallelism = 32;
// const int kLastLevelCacheSize = 16 * 1024 * 1024;
// const int kBalance = 40;
// MachineParams machine_params(kParallelism, kLastLevelCacheSize, kBalance);
//
// The arguments to MachineParams are the maximum level of parallelism
// available, the size of the last-level cache (in KB), and the ratio
// between the cost of a miss at the last level cache and the cost
// of arithmetic on the target architecture, in that order.
// Note that when using the auto-scheduler, no schedule should have
// been applied to the pipeline; otherwise, the auto-scheduler will
// throw an error. The current auto-scheduler cannot handle a
// partially-scheduled pipeline.
// If HL_DEBUG_CODEGEN is set to 3 or greater, the schedule will be dumped
// to stdout (along with much other information); a more useful way is
// to add "schedule" to the -e flag to the Generator. (In CMake and Bazel,
// this is done using the "extra_outputs" flag.)
// The generated schedule that is dumped to file is an actual
// Halide C++ source, which is readily copy-pasteable back into
// this very same source file with few modifications. Programmers
// can use this as a starting schedule and iteratively improve the
// schedule. Note that the current auto-scheduler is only able to
// generate CPU schedules and only does tiling, simple vectorization
// and parallelization. It doesn't deal with line buffering, storage
// reordering, or factoring reductions.
// At the time of writing, the auto-scheduler will produce the
// following schedule for the estimates and machine parameters
// declared above when run on this pipeline:
//
// Var x_i("x_i");
// Var x_i_vi("x_i_vi");
// Var x_i_vo("x_i_vo");
// Var x_o("x_o");
// Var x_vi("x_vi");
// Var x_vo("x_vo");
// Var y_i("y_i");
// Var y_o("y_o");
//
// Func Ix = pipeline.get_func(4);
// Func Iy = pipeline.get_func(7);
// Func gray = pipeline.get_func(3);
// Func harris = pipeline.get_func(14);
// Func output1 = pipeline.get_func(15);
// Func output2 = pipeline.get_func(16);
//
// {
// Var x = Ix.args()[0];
// Ix
// .compute_at(harris, x_o)
// .split(x, x_vo, x_vi, 8)
// .vectorize(x_vi);
// }
// {
// Var x = Iy.args()[0];
// Iy
// .compute_at(harris, x_o)
// .split(x, x_vo, x_vi, 8)
// .vectorize(x_vi);
// }
// {
// Var x = gray.args()[0];
// gray
// .compute_at(harris, x_o)
// .split(x, x_vo, x_vi, 8)
// .vectorize(x_vi);
// }
// {
// Var x = harris.args()[0];
// Var y = harris.args()[1];
// harris
// .compute_root()
// .split(x, x_o, x_i, 256)
// .split(y, y_o, y_i, 128)
// .reorder(x_i, y_i, x_o, y_o)
// .split(x_i, x_i_vo, x_i_vi, 8)
// .vectorize(x_i_vi)
// .parallel(y_o)
// .parallel(x_o);
// }
// {
// Var x = output1.args()[0];
// Var y = output1.args()[1];
// output1
// .compute_root()
// .split(x, x_vo, x_vi, 8)
// .vectorize(x_vi)
// .parallel(y);
// }
// {
// Var x = output2.args()[0];
// Var y = output2.args()[1];
// output2
// .compute_root()
// .split(x, x_vo, x_vi, 8)
// .vectorize(x_vi)
// .parallel(y);
// }
} else {
// This is where you would declare the schedule you have written by
// hand or paste the schedule generated by the auto-scheduler.
// We will use a naive schedule here to compare the performance of
// the autoschedule with a basic schedule.
gray.compute_root();
Iy.compute_root();
Ix.compute_root();
}
}
private:
Var x{"x"}, y{"y"}, c{"c"};
Func gray, Iy, Ix, Ixx, Iyy, Ixy, Sxx, Syy, Sxy, det, trace, harris;
};
// As in lesson 15, we register our generator and then compile this
// file along with tools/GenGen.cpp.
HALIDE_REGISTER_GENERATOR(AutoScheduled, auto_schedule_gen)
// After compiling this file, see how to use it in
// lesson_21_auto_scheduler_run.cpp
