macOS wifi ping spikes

Before we start:

• I’m presuming that by “spikes” you’re referring to the sections of increased latency.

• Also, make sure to read Wi-Fi Fundamentals because I’ll assume terms from there.

Most Wi-Fi hardware only has a single radio, and that radio must be tuned to a specific channel. Thus, the hardware can only work on one channel at a time.

However, there are situations where a STA need to switch channels. For example:

• When actively scanning for networks

• When an Apple STA is coordinating peer-to-peer Wi-Fi work

While it’s on that temporary channel, the STA can’t be on the channel it’s using to communicating with the AP, and thus you see spikes in latency.

If you want to investigate this further you should read Investigating Network Latency Problems. That shows how to isolate the cause of the latency to one specific subsystem. And, in the C and D case, you can use a Wi-Fi level packet trace to see what’s really happening on the ‘wire’.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Hmm, what do you think about switching the Synergy protocol to UDP?

what do you think about switching the Synergy protocol to UDP?

I presume you’re asking about what effect this will have on this specific latency issue? That really depends on the cause of the latency. If it is caused by channel switching, changing to UDP won’t have any effect.

It’s a common misconception that UDP has lower latency than TCP. From a latency perspective the only benefit that UDP has is that, if the network drops packet N, you don’t have to wait for a retransmissions before you see packet N+1. In your case, however, there’s no indication that packets are being dropped (which makes sense because Wi-Fi has its own link-level flow controller and retransmission mechanism).

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

I am also seeing this annoying problem on my latest gen MacBook Pro running 10.13.4, and it is affecting basic ssh sessions in terminal to the point of making them very unresponsive and frustrating to use at times..

It doesn't happen on other platforms, so Mr. Eskimo, Instead of finding excuses please ESCALATE THIS PROBLEM so that it gets properly investigated and fixed ASAP.

Marc

The problem is even better illustrated with a shorter interval value when pinging a local peer (such as the default gateway IP):

% ping -i 0.1 <IP_of_local_peer>

Then simultaneously starting an application such as Google Earth Pro causes not only increased latency but many request timeouts.

Marc

I have similar problem with slow ssh connection. Moreover, ping depends on interval value. If you soluted your problem, can you help me?

Mikhail

No solution yet. I'm astonished that this major bug still hasn't been resolved. It's still present even in the latest 10.14.1 beta.

I suspect that there is an interaction between apps such as Google Earth constantly querying for geolocation which leads to wifi scans which then cause the increased latency and packet loss on the wifi interface.

Perhaps even having browser windows open on sites that constantly poll for user location could also induce scans causing the same detrimental effect on wifi performance / latency / packet loss .

Apple, could you please FIX THIS PROBLEM ? It is a significant issue !

turns out Google Earth is a QT app. QT has a "bearer" plugin which can frequently request wifi scans, killing network performance. See:

https://bugreports.qt.io/browse/QTBUG-65586?gerritReviewStatus=All

and https://lostdomain.org/2017/06/17/qt-qnetworkaccessmanager-causing-latency-spikes-on-wifi/

Until Apple and QT developers get their act together, possible workarounds are setting the QT_BEARER_POLL_TIMEOUT environment variable to -1 or disabling the wlan bearer plugin altogether

in the QT app.

(for Google Earth Pro: "sudo chmod 0 /Applications/Google\ Earth\ Pro.app/Contents/plugins/bearer/libqcorewlanbearer.dylib")

I agree that it's probably wifi scanning that causes the latency. It seems that the locationd process triggers this approximately once a minute. If you start a ping in the terminal:

ping -i 0.25 192.168.1.1 --apple-time

...and watch the activity in Console.app, you'll notice that the ping response time rises as described just as locationd starts doing it's once-per-minute update. If you disable Location Services in the Privacy pref pane the periodic ping latency issues go away completely.

This latency causes major issues in audio quality with apps like GoToMeeting and causes video corruption and lag in streaming video game apps like Google's Project Stream. These issues go away when locationd isn't scanning!

Seems like there's a bug here somewhere in locationd... if it's not possible to avoid the latency during a wifi scan then perhaps locationd needs to either skip those altogether or perform them far less often. As it is today, I need to disable Location Services on my MBP if I'm joining a conference call on wifi.

Seems like there's a bug here somewhere in

locationd

.

If this problem is causing you significant grief that you should file a bug about it. Make sure to include the extra Wi-Fi logging info per the instructions on our Bug Reporting > Profiles and Logs.

Please post your bug number, just for the record.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Dear Eskimo,

rdrom, myself and others have extensively described the issue. Is that not sufficient for Apple to take action? You are the Apple employee, please do your work, file whatever bug report(s) are needed and above all, have this long standing issue fixed once and for all.

Is that not sufficient for Apple to take action?

It is best if you file your own bug reports because:

• You are the one seeing the problem, so you can describe it accurately

• If Wi-Fi Engineering has follow-up questions about the issue, they can contact you directly

• You can see the status of bug reports that you file

You are the Apple employee, please do your work …

The vast majority of my “work” involves responding to official DTS tech support incidents [1]. My time here on DevForums is roughly split 50:50 between my work time and my personal time. I choose to spend that time answering questions because I think that’s a more valuable use of that time than filing bug reports.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

[1] You can learn more about this service on our page on the developer web site.

Even if location services are disabled, wifi scanning can destroy wireless performance. Scanning will essentially pause communications on your current wifi connection, as the hardware has to hop to other channels to scan for available access points. Depending on how long this takes, you could see an adverse impact on your current connection.

Applications and plugins can trigger this behavior by trying to interact with the locationd service, such as web browsers or QuickTime (it apparently has known bugs that will cause the application using qt libraries to trigger wifi scanning). This will manifest itself as frequent or periodic ping spikes and streaming performance drops (audio or video conference calling will drop quality or cut out entirely).

Video and voice calling, particularly over wireless, can be severely impacted. You should disable all wireless devices and use ethernet only if you require anything related to audio or video over the network. If your office is wireless only, you may need to re-evaluate your hardware / OS options.

One way to confirm this is to do the following:

1) open Apple's "Console" Application

2) add "scan" as asearch term to the top-right

3) scroll to the bottom of the log pane so new events show up at the bottom as they occur

4) open the terminal / iterm2 app and ping either '1.1.1.1' or your local router

5) click on your wireless icon and see if your ping lag spikes occur at the same time as the "locationd" messages

If you have location services disabled, you will see the following:

default 12:01:58.360773 -0400 locationd WIFI_LOC: location services are disabled, ignore scan result

default 12:01:58.907701 -0400 locationd WIFI_LOC: location services are disabled, ignore scan result

default 12:01:59.469546 -0400 locationd WIFI_LOC: location services are disabled, ignore scan result

default 12:02:00.089787 -0400 locationd WIFI_LOC: location services are disabled, ignore scan result

default 12:02:00.922026 -0400 locationd WIFI_LOC: location services are disabled, ignore scan result

If location services are enabled, you will see the following:

default 12:03:25.995118 -0400 locationd WIFI_LOC: onWifiNotification, notification, <private>, kNotificationScan, scanType, <private>, <private>, inject, <private>, inProg, <private>

default 12:03:25.995167 -0400 locationd WIFI_LOC: scan result, scanType, <private>, <private>, currentRequest, <private>

default 12:03:26.546485 -0400 locationd WIFI_LOC: onWifiNotification, notification, <private>, kNotificationScan, scanType, <private>, <private>, inject, <private>, inProg, <private>

default 12:03:26.546536 -0400 locationd WIFI_LOC: scan result, scanType, <private>, <private>, currentRequest, <private>

default 12:03:26.705880 -0400 locationd WIFI_LOC: processScanResult, aps, <private>, fIsUseNetworkLocationProvider, <private>, fIsUseTileManager, <private>

. . .

The ping latency may improve with location services disabled, but the problem likely will not be eliminated. You must identify the application, service, or plugin that is triggering wifi scanning.

Hopefully someone from Apple can chime in with a simple method of doing so (like monitoring / tracing to capture apps). In the event they don't respond, you might try taking a look at capturing additional logging...

https://www.howtogeek.com/211034/troubleshoot-and-analyze-your-mac%E2%80%99s-wi-fi-with-the-wireless-diagnostics-tool/

https://superuser.com/questions/585473/debugging-osx-airport-wifi-connection

Related links:

https://superuser.com/questions/1142798/experiencing-high-latency-on-wifi-every-other-second-with-macos-sierra

https://superuser.com/questions/1142798/experiencing-high-latency-on-wifi-every-other-second-with-macos-sierrahttps://apple.stackexchange.com/questions/310218/stop-destroying-network-performance-every-time-an-app-scans-for-wifi-networks/312388

https://lostdomain.org/2017/06/17/qt-qnetworkaccessmanager-causing-latency-spikes-on-wifi/

https://bugreports.qt.io/browse/QTBUG-65586?gerritReviewStatus=All

https://discussions.apple.com/thread/8523377

Thank you! You saved my day.

Here is what I did:

System Preferences -> Security and Privacy -> Location Services (left) -> System Services (at the bottom of the list) -> Details -> Turn off "Wi-Fi Networking"

And after that - reboot the computer.

The problem went away.

+1 on this issue. I've been chasing the ping-spikes for about a month after moving a new office. I hadn't experienced this in other networks. However, at this location, I was having high-latency spikes every ~5min. Very frustrating when you're in meetings and things freeze. Even worse, I was also experiencing packet loss when this happened.

In my case, similarly, the fix was to fully turn off location services. I don't want to given apps like Find My Mac, but I can't live with the ping spikes.

@Eskimo - can you let me know if this is already logged as a bug? Otherwise, I'll be happy to create one.