Sub-millisecond GC pauses

[Austin Clements]

10 millisecond pauses are so 2015.

Today I submitted changes to the garbage collector that make typical worst-case stop-the-world times less than 100 microseconds. This should particularly improve pauses for applications with many active goroutines, which could previously inflate pause times significantly.

If you're already experimenting with master, we would love it if you could try this out and hammer on the new algorithm. We're particularly interested in any significant performance regressions, pause times significantly longer than 100 microseconds, or any crashes. And, of course, we'd love to hear about any improvements you see. :)

If you do encounter problems, please also test at commit d70b0fe or earlier, which is just before the algorithm changes started going in.

There are still known issues with the garbage collector interrupting individual goroutines for too long. We've made improvements to this for Go 1.8 and will continue to improve it, but this change is specifically about the garbage collector interrupting the whole application.

If you're curious, the full design document is at https://github.com/golang/proposal/blob/master/design/17503-eliminate-rescan.md

[jfcg...@gmail.com]

This brings Go well into real-time realm.
I think avionics/mission-critical apps will/can switch to Go very soon.

[Mikael Gustavsson]

Wow, that sounds amazing! For realtime graphics 10ms means you'll likely miss a frame, while 100µs isn't even worth caring about.

[the...@gmail.com]

Avionics? C'mon now..

Nice efficiency gain though

[loui...@gmail.com]

This is very exciting for the MEG/EEG field too, I think.  Typical experiments require ms-level control of events (a serious sore-spot for the python scientific ecosystem).

This is pretty exciting!  Kudos and thanks to all involved!

[lini.g...@gmail.com]

Sounds cool! I am pulling the git master right now and I am going to test it against my worst case scenario with very large in-memory maps
Thanks for clarifying this point: "...There are still known issues with the garbage collector interrupting individual goroutines for too long..."
I think I am hitting this barrier again, but worth trying

[val...@gmail.com]

Below are our results before and after the switch to new GC in production serving up to 200K qps per host:

Service 1 - http://grafana.videe.tv/dashboard/snapshot/TgwVzDDQq2Z4P5PJK4oa7uxb695LXLsU 

Service 2 - http://grafana.videe.tv/dashboard/snapshot/26fww16dGTX6JJMPdPvhPHQuov02Iz49 

The Service 1 allocates more than the Service 2, so STW pauses are higher there. But STW pause duration dropped by an order of magnitude on both services.

We see ~20% increase in CPU usage spent in GC after the switch on both services.

[Austin Clements]

On Sat, Oct 29, 2016 at 3:29 PM, <val...@gmail.com> wrote:

Below are our results before and after the switch to new GC in production serving up to 200K qps per host:

Service 1 - http://grafana.videe.tv/dashboard/snapshot/TgwVzDDQq2Z4P5PJK4oa7uxb695LXLsU 

Service 2 - http://grafana.videe.tv/dashboard/snapshot/26fww16dGTX6JJMPdPvhPHQuov02Iz49 

The Service 1 allocates more than the Service 2, so STW pauses are higher there. But STW pause duration dropped by an order of magnitude on both services.

We see ~20% increase in CPU usage spent in GC after the switch on both services.

Those STW times look great, but that's much more CPU than I would have expected. Could you file an issue, preferably with more details on where you're seeing the increase and before/after profiles if you can, and cc me (GitHub: aclements)? Thanks!

[Damian Gryski]

I've seen a bunch of references to this "20% CPU increase" as the cost of the new low-latency GC, even though it was clearly identified as a bug.

Did an issue ever get filed for this?

Damian

[Austin Clements]

Hi Damian. Aliaksandr's 20% relative increase turned out to be a 2% absolute increase in GC CPU, so we decided an issue wasn't needed.

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