Hi All,
Trying 8.7.1 and TOT, I discovered a subtle performance degradation for H2
transfers vs 8.6.0, which I would like to report.
It is subtle because it is mostly visible on low-end hardware platforms with
weak CPUs in cases when a client application needs to perform heavy processing
of incoming data (i.e. JSON parsing and processing).
I stepped on small performance degradation with 8.7.1 when I analyzed overall
H2 transfer time metrics in my application which included total transfer
process time (download + processing).
As it turned out, 8.7.1 (and TOT) processes H2 transfers with a larger number
of write callbacks than 8.6.0, and with smaller chunk sizes.
Here is the illustration for two H2 multiplexed 1MB transfers downloaded over
LAN:
8.6.0, 2 H2, LAN: **** chunks=134, min_size=36, max_size=16384, avg_size=15650,
time=32ms,
<size:count map> [36:1, 117:1, 149:1, 230:1, 567:2, 16100:2, 16375:122,
16384:4]
8.7.1, 2 H2, LAN: **** chunks =146, min_size=45, max_size=16375,
avg_size=14364, time=36ms,
<size:count map> [45:8, 158:8, 576:2, 16217:8, 16330:8, 16375:112]
As we can see from the example data, 8.7.1 had smaller data chunks on average
(14364 vs 15650),
the total number of chunks was greater (146 vs 134), and the full
CURL_MAX_WRITE_SIZE (16384) was never used.
(A similar picture if I use just one H2 download and slower speeds).
While it is not an issue for fast CPUs, a bigger number of write callbacks with
smaller sizes might affect overall transfer performance on slow CPUs.
So, I thought it could be helpful to provide feedback from this perspective.
Thanks,
Dmitry Karpov
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