daemon/stats: more resilient cpu sampling#36519
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To avoid noise in sampling CPU usage metrics, we now sample the system usage closer to the actual response from the underlying runtime. Because the response from the runtime may be delayed, this makes the sampling more resilient in loaded conditions. In addition to this, we also replace the tick with a sleep to avoid situations where ticks can backup under loaded conditions. The trade off here is slightly more load reading the system CPU usage for each container. There may be an optimization required for large amounts of containers but the cost is on the order of 15 ms per 1000 containers. If this becomes a problem, we can time slot the sampling, but the complexity may not be worth it unless we can test further. Unfortunately, there aren't really any good tests for this condition. Triggering this behavior is highly system dependent. As a matter of course, we should qualify the fix with the users that are affected. Signed-off-by: Stephen J Day <[email protected]>
boaz0
reviewed
Mar 8, 2018
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Why did you use time.Sleep and not kept using range time.Tick?
Unless I am wrong, they are similar functionality wise.
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If it takes more than the interval time, the ticks backup and cause a burst of sampling, making the issue worse.
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LGTM |
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LGTM 🏆 |
Codecov Report
@@ Coverage Diff @@
## master #36519 +/- ##
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Coverage ? 34.66%
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Files ? 613
Lines ? 45414
Branches ? 0
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Hits ? 15742
Misses ? 27615
Partials ? 2057 |
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To avoid noise in sampling CPU usage metrics, we now sample the system
usage closer to the actual response from the underlying runtime. Because
the response from the runtime may be delayed, this makes the sampling
more resilient in loaded conditions. In addition to this, we also
replace the tick with a sleep to avoid situations where ticks can backup
under loaded conditions.
The trade off here is slightly more load reading the system CPU usage
for each container. There may be an optimization required for large
amounts of containers but the cost is on the order of 15 ms per 1000
containers. If this becomes a problem, we can time slot the sampling,
but the complexity may not be worth it unless we can test further.
Unfortunately, there aren't really any good tests for this condition.
Triggering this behavior is highly system dependent. As a matter of
course, we should qualify the fix with the users that are affected.
Signed-off-by: Stephen J Day [email protected]