some questions about the flamegraph of quiche-server

[yejingx]

When I tested quic-server, I found that a lot of time was spent in quiche::h3::qpack::huffman::Decoder::decode4. Why are so many memcpys generated here?

[Suldeaked]

i don't know try to find out what is going on

On Tue, Oct 25, 2022, 10:10 AM yejingx @.***> wrote:

When I tested quic-server, I found that a lot of time was spent in quiche::h3::qpack::huffman::Decoder::decode4. Why are so many memcpys generated here?

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[LPardue]

@yejingx can you provide any more information about your setup please? What is the client, what headers are being sent to the server, have you got a pcap with decryption keys that you can share?

[yejingx]

@LPardue the setup:

1. cargo build to build the master branch
2. run quiche-server with default parameters
3. test the server with h2load

   h2load --npn-list h3 -D 100 -c 100 -t 4 https://127.0.0.1:4433/hello

4. Start flamegraph to collect the profile of quiche-server

   flamegraph --pid 3419385

   3419385 is the pid of the running quiche-server.

here is the generated flamegraph:

and the result of h2load:

The reason why all requests failed is that the path /hello is 404

[LPardue]

Thank you for the detailed reproduction steps. This will help us investigate.

[yejingx]

@LPardue Have you reproduced it? The flame graph is really weird, I don't know if it's a bug of quiche-server or something is wrong with the flamegraph tool.

[junhochoi]

All h2load requests are failing - you need to fix it first. After that, please try with a release build.

[yejingx]

@junhochoi As I mentioned above, all h2load requests failed because of the path /hello is not exist.

I retried with an existing /hello path, all requests are 200 now(also, I don't think it should be so even if all the requests fail). The result is shown below:

The commands to reproduce:

1. run the server

   flamegraph -- ../target/debug/quiche-server --root <root path>

2. start h2load

   h2load --npn-list h3 -D 20 -c 1 -t 1 -m 1 https://127.0.0.1:4433/hello

The version I used to test is 0.16.0