masaori335 opened a new pull request #8052:
URL: https://github.com/apache/trafficserver/pull/8052
# Proposal
Add new TSMimeHdrFieldFast* APIs which don't allocate `MIMEFieldSDKHandle`.
```
tsapi size_t TSMimeHdrFieldFastMLocSize();
tsapi TSReturnCode TSMimeHdrFieldFastFind(TSMBuffer bufp, TSMLoc hdr, const
char *name, int length, TSMLoc *locp);
tsapi TSReturnCode TSMimeHdrFieldFastCreateNamed(TSMBuffer bufp, TSMLoc
mh_mloc, const char *name, int name_len, TSMLoc *locp);
tsapi TSReturnCode TSMimeHdrFieldFastNextDup(TSMBuffer bufp, TSMLoc hdr,
TSMLoc field, TSMLoc *locp);
```
The changes in `plugins/header_rewrite/operators.cc` demonstrate how to use
them. Currently, `add-header`, `set-header` and `rm-header` are improved. If we
agree with this approach, I'll expand support later.
# Background
@c-taylor said, "every new header-rewrite condition you add, loses about
20,000 RPS". We looked at perf and the bottleneck is `MIMEFieldSDKHandle`
allocation in `TSMimeHdrField*` APIs.
```
- 1.88% [ET_NET 5] libtscore.so.8.1.2 [.] freelist_new
freelist_new
- ink_freelist_new
- 1.87% ClassAllocator<MIMEFieldSDKHandle>::alloc (inlined)
- sdk_alloc_field_handle (inlined)
- 1.20% TSMimeHdrFieldCreateNamed
0.67% TSMimeHdrFieldFind
```
It looks like we can avoid these expensive allocations by using a dynamic
buffer on the stack. Because the allocated memory is released immediately. This
change is a bit hacky but no allocation on the heap is the best choice from the
performance perspective.
- e.g. `TSMimeHdrFieldCreateNamed` and `add-header` of header_rewrite
https://github.com/apache/trafficserver/blob/3412c4f69552b10779cfe0ce1bc6a71971734491/src/traffic_server/InkAPI.cc#L3148
https://github.com/apache/trafficserver/blob/3412c4f69552b10779cfe0ce1bc6a71971734491/plugins/header_rewrite/operators.cc#L613-L618
# Benchmark
@c-tayor did a benchmark with several traffic patterns. We got 50 - 70 %
improvement with this change on Keep-Alive traffic. No big difference on no
Keep-Alive traffic but it's other issues.
## Conditions
- AMD EPYC 7502P
- ATS 8.1.2, 28 thread, affinity 3
- header_rewrite plugin with 2 `add-header` & 2 `set-header`
- openssl-1.1.1x
## Before
```
noKA: 108900
noKA-tls: 13500
KA: 112400
KA-tls: 114700
KA-tls-h2: 116300
```
## After
```
noKA: 109100
noKA-tls: 13400
KA: 184900
KA-tls: 196700
KA-tls-h2: 178000
```
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