Node.js async/await issue reveal - blocked event loop

async_await.js

const TEST_TIMEOUT = 1;

(async () => {
    const raw = () => {
        let count = 0;
        const start = process.hrtime();

        while (process.hrtime(start)[0] < TEST_TIMEOUT) {
            for(let j = 0; j < 128; ++j) {
                ++count;
            }
        }
        
        return count;
    };

    const async_f = async () => {
        let count = 0;
        const start = process.hrtime();
        
        const step = async () => {};
        
        while (process.hrtime(start)[0] < TEST_TIMEOUT) {
            for(let j = 0; j < 128; ++j) {
                await step();
                ++count;
            }
        }
        
        return count;
    };
    
    const async_double = async () => {
        const start = process.hrtime();
        
        const f = async (start) => {
            let count = 0;

            const step = async () => {
                ++count;
            };
            
            while (process.hrtime(start)[0] < TEST_TIMEOUT) {
                for(let j = 0; j < 128; ++j) {
                    await step();
                }
            }
            
            return count;
        };
        
        return Promise.all([
            f(start),
            f(start)
        ]);
    };
    
    const event_loop = () => new Promise(resolve => {
        let count = 0;
        const start = process.hrtime();
        
        const fire = () => {
            ++count;
        };
        
        const iter = () => {
            ++count;
            
            if (process.hrtime(start)[0] >= TEST_TIMEOUT) {
                resolve(count);
                return;
            }
            
            for(let j = 0; j < 128; ++j) {
                setImmediate(fire);
            }
            
            setImmediate(iter);
        };
        
        setImmediate(iter);
    });
    
    const async_event_loop = async () => {
        const start = process.hrtime();
        
        const f = async (start) => {
            let count = 0;

            const step = async () => {
                ++count;
            };
            
            while (process.hrtime(start)[0] < TEST_TIMEOUT) {
                for(let j = 0; j < 128; ++j) {
                    await step();
                }
            }
            
            return count;
        };
        
        const el = (start) => new Promise(resolve => {
            let count = 0;
            
            const fire = () => {
                ++count;
            };
            
            const iter = () => {
                ++count;
                
                if (process.hrtime(start)[0] >= TEST_TIMEOUT) {
                    resolve(count);
                    return;
                }
                
                for(let j = 0; j < 128; ++j) {
                    setImmediate(fire);
                }
                
                setImmediate(iter);
            };
            
            setImmediate(iter);
        });
        
        return Promise.all([
            f(start),
            el(start)
        ]);
    };
    
    const raw_res = raw();
    const async_one_res = await async_f();
    const async_double_res = await async_double();
    const event_loop_res = await event_loop();
    const async_event_loop_res = await async_event_loop();
    
    console.log(`Raw count: ${raw_res}`);
    console.log(`Async count: ${async_one_res}`);
    console.log(`Async parallel count: ${async_double_res}`);
    console.log(`Event loop: ${event_loop_res}`);
    console.log(`Async + Event loop: ${async_event_loop_res}`);
    console.log(`END`);
})();

Results v10:

$ nodeVer=10 cte node async_await.js
Exec: ~/.nvm/versions/node/v10.11.0/bin/node async_await.js
Raw count: 27436800
Async count: 3477504
Async parallel count: 2026496,2026496
Event loop: 5846797
Async + Event loop: 3890688,1
END

Results v8:

$ nodeVer=8 cte node async_await.js
Exec: ~/.nvm/versions/node/v8.12.0/bin/node async_await.js
Raw count: 27528960
Async count: 2431232
Async parallel count: 1285504,1285504
Event loop: 918352
Async + Event loop: 2548352,1
END