Hello!

On Thu, Dec 02, 2021 at 02:05:52PM +0200, Lyuben Stoev wrote:

> Hello,
>     I have tested the nginx with the patch
> https://hg.nginx.org/nginx/rev/65946a191197 (SSL: SSL_sendfile() support
> with kernel TLS.) following the nginx blog article
> https://www.nginx.com/blog/improving-nginx-performance-with-kernel-tls/
> And it sort of works, but I have bad performance when making HTTP/2
> requests. If I made a HTTP/1.1 request there is 30-35% increase in
> performance as the Nginx blog article stated, but when I changed the
> request to use HTTP/2 the request was 40% slower than an ordinary nginx
> without KTLS enabled. Does anyone have such perfomance degradation with
> nginx KTLS and HTTP/2? I am using generic setup - Ubuntu 20.04.3 LTS and
> kernels 5.8.0-63-generic (the same results are with 5.4.0-91-generic).
> The nginx vritual host is the same as in the Nginx blog article with
> exception of adding http2 to the listen! OpenSSL 3.0.0 and nginx 1.21.4
> are used.
> The KTLS seems to work, because the strace and debug logs show it. Just
> the sstrange thing is when using HTTP2, the sendfile syscalls look:
>     write(39, "\0 \0\0\0\0\0\0\1", 9)       = 9
>     sendfile(39, 131, [1418218] => [1426410], 8192) = 8192
>     write(39, "\0 \0\0\0\0\0\0\1", 9)       = 9
>     sendfile(39, 131, [1426410] => [1434602], 8192) = 8192
>     write(39, "\0 \0\0\0\0\0\0\1", 9)       = 9
>     sendfile(39, 131, [1434602] => [1442794], 8192) = 8192
>     write(39, "\0 \0\0\0\0\0\0\1", 9)       = 9
>     sendfile(39, 131, [1442794] => [1450986], 8192) = 8192
>     write(39, "\0 \0\0\0\0\0\0\1", 9)       = 9
>     sendfile(39, 131, [1450986] => [1459178], 8192) = 8192
>     write(39, "\0 \0\0\0\0\0\0\1", 9)       = 9
>     sendfile(39, 131, [1459178] => [1467370], 8192) = 8192
>
> It is always 8K and there are thousands of sendfile syscalls....

That's expected, because of HTTP/2 framing. Unfortunately, HTTP/2
isn't designed to work with sendfile(), and sending large files
over HTTP/2 require a lot of sendfile() syscalls. In general, for
HTTP/2 it is better to keep sendfile() disabled.

--
Maxim Dounin
http://mdounin.ru/
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