The two recent commits below each added one flag to h2c but omitted to
update the __APPEND_FLAG macro used by dev/flags so they are not
properly decoded:
3dd963b35 ("BUG/MINOR: mux-h2: fix http-request and http-keep-alive timeouts again")
68d02e5fa ("BUG/MINOR: mux-h2: make up other blocked streams upon removal from list")
This can be backported along with these commits.
Stefan Behte reported that since commit f279a2f14 ("BUG/MINOR: mux-h2:
refresh the idle_timer when the mux is empty"), the http-request and
http-keep-alive timeouts don't work anymore on H2. Before this patch,
and since 3e448b9b64 ("BUG/MEDIUM: mux-h2: make sure control frames do
not refresh the idle timeout"), they would only be refreshed after stream
frames were sent (HEADERS or DATA) but the patch above that adds more
refresh points broke these so they don't expire anymore as long as
there's some activity.
We cannot just revert the fix since it also addressed an isse by which
sometimes the timeout would trigger too early and provoque truncated
responses. The right approach here is in fact to only use refresh the
idle timer when the mux buffer was flushed from any such stream frames.
In order to achieve this, we're now setting a flag on the connection
whenever we write a stream frame, and we consider that flag when deciding
to refresh the buffer after it's emptied. This way we'll only clear that
flag once the buffer is empty and there were stream data in it, not if
there were no such stream data. In theory it remains possible to leave
the flag on if some control data is appended after the buffer and it's
never cleared, but in practice it's not a problem as a buffer will always
get sent in large blocks when the window opens. Even a large buffer should
be emptied once in a while as control frames will not fill it as much as
data frames could.
Given the patch above was backported as far as 2.6, this patch should
also be backported as far as 2.6.
An interesting issue was met when testing the mux-to-mux forwarding code.
In order to preserve fairness, in h2_snd_buf() if other streams are waiting
in send_list or fctl_list, the stream that is attempting to send also goes
to its list, and will be woken up by h2_process_mux() or h2_send() when
some space is released. But on rare occasions, there are only a few (or
even a single) streams waiting in this list, and these streams are just
quickly removed because of a timeout or a quick h2_detach() that calls
h2s_destroy(). In this case there's no even to wake up the other waiting
stream in its list, and this will possibly resume processing after some
client WINDOW_UPDATE frames or even new streams, so usually it doesn't
last too long and it not much noticeable, reason why it was left that
long. In addition, measures have shown that in heavy network-bound
benchmark, this exact situation happens on less than 1% of the streams
(reached 4% with mux-mux).
The fix here consists in replacing these LIST_DEL_INIT() calls on
h2s->list with a function call that checks if other streams were queued
to the send_list recently, and if so, which also tries to resume them
by calling h2_resume_each_sending_h2s(). The detection of late additions
is made via a new flag on the connection, H2_CF_WAIT_INLIST, which is set
when a stream is queued due to other streams being present, and which is
cleared when this is function is called.
It is particularly difficult to reproduce this case which is particularly
timing-dependent, but in a constrained environment, a test involving 32
conns of 20 streams each, all downloading a 10 MB object previously
showed a limitation of 17 Gbps with lots of idle CPU time, and now
filled the cable at 25 Gbps.
This should be backported to all versions where it applies.
Some fields in h2c structures are not used: .mfl, .mft and .mff. Just remove
them.
.msi field is also removed. It is tested but never set, except when a H2
connection is initialized. It also means h2c_mux_busy() function is useless
because it always returns 0 (.msi is always -1). And thus, by transitivity,
H2_CF_DEM_MBUSY is also useless because it is never set. So .msi field,
h2c_mux_busy() function and H2C_MUX_BUSY flag are removed.
Similarly to the H1 multiplexer, H2_CF_ERR_PENDING is now used to report an
error when we try to send data and H2_CF_ERROR to report an error when we
try to read data. In other funcions, we rely on these flags instead of
connection ones. Only H2_CF_ERROR is considered as a final error.
H2_CF_ERR_PENDING does not block receive attempt.
In addition, we rely on H2_CF_RCVD_SHUT flag to test if a read0 was received
or not.
The new functions h2c_show_flags() and h2s_show_flags() decode the flags
state into a string, and are used by dev/flags:
$ ./dev/flags/flags h2c 0x0600
h2c->flags = H2_CF_DEM_IN_PROGRESS | H2_CF_DEM_SHORT_READ
$ ./dev/flags/flags h2s 0x7003
h2s->flags = H2_SF_HEADERS_RCVD | H2_SF_OUTGOING_DATA | H2_SF_HEADERS_SENT \
| H2_SF_ES_SENT | H2_SF_ES_RCVD
Originally in 1.8 we wanted to have an independent mux that could possibly
be disabled and would not impose dependencies on the outside. Everything
would fit into a single C file and that was fine.
Nowadays muxes are unavoidable, and not being able to easily inspect them
from outside is sometimes a bit of a pain. In particular, the flags utility
still cannot be used to decode their flags.
As a first step towards this, this patch moves the flags and enums to
mux_h2-t.h, as well as the two state decoding inline functions. It also
dropped the H2_SS_*_BIT defines that nobody uses. The mux_h2.c file remains
the only one to include that for now.
