730163 - Add telemetry for time spent waiting on cache service lock

Status: RESOLVED FIXED

(Core :: Networking: Cache, defect)

Description

[u408661]

This will help us determine how big of a problem the global lock actually is, and will also help us determine when we're making things better and by how much.

Comment 1

[u408661]

Attachment: patch

I'm not tied to having 2 different telemetry entries for main thread vs. non-main thread, but I thought it might be useful to know how long we block the main thread vs other stuff on the cache thread.

Comment 2

[Honza Bambas (:mayhemer)]

Nick, why not to add the telemetry right inside nsCacheService::Lock() ?

Comment 3

[u408661]

Comment on attachment 601049 [details] [diff] [review]
patch

Honza, I have no good reason, and looking at the code, I realized there's at least one place outside the autolock where we do actually call nsCacheService::Lock directly, so in there is probably a better place to put the telemetry. I'll update the patch.

Comment 4

[u408661]

Attachment: patch

OK, here's the same patch with the telemetry accumulation pushed down into nsCacheService::Lock as Honza suggested.

Comment 5

[u408661]

Attachment: patch

Update commit message w/r=michal. carry forward r+

Comment 6

[u408661]

Try is good https://tbpl.mozilla.org/?tree=Try&rev=c0a96ed0beb7

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/58715a30c0da

Comment 8

[Honza Bambas (:mayhemer)]

I believe the times will be about a millisecond if even that long.  I observed long times waiting only short after start when the cache warms up.

Comment 9

[Matt Brubeck (:mbrubeck)]

https://hg.mozilla.org/mozilla-central/rev/58715a30c0da