Hello,
As subject says, I was wondering if it is possible for concurrent part of
GC process to still stall program execution. And if there are certain type
of
things that may still block.
I am wondering about this, because we see this behavior in production both
with Go 1.5 and 1.6.
Here is example of GODEBUG=gctrace=1 output of Go 1.5 program:
gc 27004 @74856.698s 1%: 0.66+115+0.15+0.27+8.1 ms clock, 5.3+115+0+47/0.016
/101+65 ms cpu, 272->277->144 MB, 279 MB goal, 8 P
gc 27005 @74859.536s 1%: 0.77+120+0.051+0.26+8.7 ms clock, 6.1+120+0+30/
0.011/117+69 ms cpu, 272->277->144 MB, 279 MB goal, 8 P
gc 27006 @74862.400s 1%: 0.92+118+0.15+0.26+7.8 ms clock, 7.3+118+0+29/0.008
/119+62 ms cpu, 272->276->144 MB, 279 MB goal, 8 P
gc 27007 @74864.392s 1%: 0.73+122+0.17+0.41+8.2 ms clock, 5.9+122+0+59/0/103
+66 ms cpu, 272->277->144 MB, 279 MB goal, 8 P
gc 27008 @74866.865s 1%: 0.72+117+0.064+0.19+7.8 ms clock, 5.7+117+0+35/
0.010/109+63 ms cpu, 272->277->144 MB, 279 MB goal, 8 P
Theoretically the STW part shouldn't exceed 10ms, however we definitely can
get requests stall for 100-130ms.
To confirm this, I ran a very simple test against running process:
for x in xrange(1000000):
t0 = time.time()
c.perform("GET", "/noop_route")
tdelta = time.time() - t0
if tdelta > 0.02:
print time.time(), "Large TDELTA:", tdelta
And saw output like this:
1468438989.77 Large TDELTA: 0.12552690506
1468438992.1 Large TDELTA: 0.137628078461
1468438994.33 Large TDELTA: 0.115905046463
1468438996.6 Large TDELTA: 0.143169164658
1468438998.83 Large TDELTA: 0.13204908371
1468439000.73 Large TDELTA: 0.10854101181
This matches GC cycles very closely, happens every ~3seconds and we see
stalls of >100ms. Also note that the '/noop_route' just goes through GOLang
standard http stack, there should be pretty much no extra or custom code in
there.
---------
We do see same behavior with Go 1.6 too (but overall GC times are lower,
but still looks like things stall during concurrent phase too). Do you have
any potential ideas what might be happening here?
Thanks
-Zviad
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