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core(lantern): use fixed times for data URLs #9932

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Nov 7, 2019
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core(lantern): use fixed times for data URLs #9932

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core(lantern): use fixed times for data URLs
patrickhulce Nov 6, 2019
e51348a
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patrickhulce Nov 6, 2019
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18 changes: 18 additions & 0 deletions lighthouse-core/lib/dependency-graph/network-node.js
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@

const BaseNode = require('./base-node.js');
const NetworkRequest = require('../network-request.js');
const URL = require('../url-shim.js');
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We've got to rename this thing at some point


class NetworkNode extends BaseNode {
/**
Expand Down Expand Up @@ -57,6 +58,23 @@ class NetworkNode extends BaseNode {
return !!this._record.fromDiskCache;
}

/**
* @return {boolean}
*/
get isNonNetworkProtocol() {
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What's up with all getters in this file? Kind of weird :)

return URL.NON_NETWORK_PROTOCOLS.includes(this._record.protocol);
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Is it useful to reuse this here vs making a new list here? There are some non network protocols we wouldn't include here (presumably eg intent wouldn't end up as a node, but this list might expand in the future)

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I'm not sure when this would actually need to diverge from our canonical set, so I'd prefer to reuse. It's true it will include things we don't actually need to test but I doubt the reverse will ever be true

}


/**
* Returns whether this network record can be downloaded without a TCP connection.
* During simulation we treat data coming in over a network connection separately from on-device data.
* @return {boolean}
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*/
get isConnectionless() {
return this.fromDiskCache || this.isNonNetworkProtocol;
}

/**
* @return {boolean}
*/
Expand Down
15 changes: 11 additions & 4 deletions lighthouse-core/lib/dependency-graph/simulator/simulator.js
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Expand Up @@ -225,8 +225,8 @@ class Simulator {

if (node.type !== BaseNode.TYPES.NETWORK) throw new Error('Unsupported');

// If a network request is cached, we can always start it, so skip the connection checks
if (!node.fromDiskCache) {
// If a network request is connectionless, we can always start it, so skip the connection checks
if (!node.isConnectionless) {
// Start a network request if we're not at max requests and a connection is available
const numberOfActiveRequests = this._numberInProgress(node.type);
if (numberOfActiveRequests >= this._maximumConcurrentRequests) return;
Expand Down Expand Up @@ -295,10 +295,17 @@ class Simulator {

let timeElapsed = 0;
if (networkNode.fromDiskCache) {
// Rough access time for seeking to location on disk and reading sequentially = 8ms + 20ms/MB
// Rough access time for seeking to location on disk and reading sequentially.
// 8ms per seek + 20ms/MB
// @see http://norvig.com/21-days.html#answers
const sizeInMb = (record.resourceSize || 0) / 1024 / 1024;
timeElapsed = 8 + 20 * sizeInMb - timingData.timeElapsed;
} else if (networkNode.isNonNetworkProtocol) {
// Estimates for the overhead of a data URL in Chromium and the decoding time for base64-encoded data.
// 2ms per request + 10ms/MB
// @see traces on https://dopiaza.org/tools/datauri/examples/index.php
const sizeInMb = (record.resourceSize || 0) / 1024 / 1024;
timeElapsed = 2 + 10 * sizeInMb - timingData.timeElapsed;
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Is this low compared to @paulirish's 10-15ms suggestion?

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yeah but I couldn't find evidence to support that much overhead on some test pages and 10-15 seemed too high compared to our read from disk estimates, @paulirish do you have any docs we could link to to support 10-15ms?

happy to use whatever we have clear evidence of

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happy to use whatever we have clear evidence of

I'd guess that @paulirish was ballparking, too, so let's call this good and we can revisit later if somehow these end up giving us bizarre lantern graphs or something (seems very unlikely :)

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yah was just ballparking. I went looking in UMA yesterday but couldnt spot a relevant histogram.

Seems fine for now. 👍

} else {
const connection = this._connectionPool.acquireActiveConnectionFromRecord(record);
const dnsResolutionTime = this._dns.getTimeUntilResolution(record, {
Expand Down Expand Up @@ -342,7 +349,7 @@ class Simulator {
const timingData = this._getTimingData(node);
const isFinished = timingData.estimatedTimeElapsed === timePeriodLength;

if (node.type === BaseNode.TYPES.CPU || node.fromDiskCache) {
if (node.type === BaseNode.TYPES.CPU || node.isConnectionless) {
return isFinished
? this._markNodeAsComplete(node, totalElapsedTime)
: (timingData.timeElapsed += timePeriodLength);
Expand Down
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