OPTIM: mux-h1: limit first read size to avoid wrapping
Before muxes were used, we used to refrain from reading past the
buffer's reserve. But with muxes which have their own buffer, this
rule was a bit forgotten, resulting in an extraneous read to be
performed just because the rx buffer cannot be entirely transferred
to the stream layer:
sendto(12, "GET /?s=16k HTTP/1.1\r\nhost: 127."..., 84, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 84
recvfrom(12, "HTTP/1.1 200\r\nContent-length: 16"..., 16320, 0, NULL, NULL) = 16320
recvfrom(12, ".123456789.12345", 16, 0, NULL, NULL) = 16
recvfrom(12, "6789.123456789.12345678\n.1234567"..., 15244, 0, NULL, NULL) = 182
recvfrom(12, 0x1e5d5d6, 15062, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
Here the server sends 16kB of payload after a headers block, the mux reads
16320 into the ibuf, and the stream layer consumes 15360 from the first
h1_rcv_buf(), which leaves 960 into the buffer and releases a few indexes.
The buffer cannot be realigned due to these remaining data, and a subsequent
read is made on 16 bytes, then again on 182 bytes.
By avoiding to read too much on the first call, we can avoid needlessly
filling this buffer:
recvfrom(12, "HTTP/1.1 200\r\nContent-length: 16"..., 15360, 0, NULL, NULL) = 15360
recvfrom(12, "456789.123456789.123456789.12345"..., 16220, 0, NULL, NULL) = 1158
recvfrom(12, 0x1d52a3a, 15062, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
This is much more efficient and uses less RAM since the first buffer that
was emptied can now be released.
Note that a further improvement (tested) consists in reading even less
(typically 1kB) so that most of the data are transferred in zero-copy, and
are not read until process_stream() is scheduled. This patch doesn't do that
for now so that it can be backported without any obscure impact.
1 file changed