From now on, the FD's update_mask only refers to local thread IDs. However,
there remains a limitation, in updt_fd_polling(), we temporarily have to
check and set shared FDs against .thread_mask, which still contains global
ones. As such, nbtgroups > 1 may break (but this is not yet supported without
special build options).
This changes the signification of each bit in the polled_mask so that
now each bit represents a local thread ID for the current group instead
of a global thread ID. As such, all tests now apply to ltid_bit instead
of tid_bit.
No particular check was made to verify that the FD's tgid matches the
current one because there should be no case where this is not true. A
check was added in epoll's __fd_clo() to confirm it never differs unless
expected (soft stop under thread isolation, or master in starting mode
going to exec mode), but that doesn't prevent from doing the job: it
only consists in checking in the group's threads those that are still
polling this FD and to remove them.
Some atomic loads were added at the various locations, and most repetitive
references to polled_mask[fd].xx were turned to a local copy instead making
the code much more clear.
The update-list needs to be per-group because its inspection is based
on a mask and we need to be certain when scanning it if a mask is for
the same thread or another one. Once per-group there's no doubt about
it, even if the FD's polling changes, the entry remains valid. It will
be needed to check the tgid though.
Note that a soft-stop or pause/resume might not necessarily work here
with tgroups>1, because the operation might be delivered to a thread
that doesn't belong to the group and whoe update mask will not reflect
one that is interesting here. We can't do better at this stage.
These old legacy pollers are not designed for this. They're still
using a shared list of events for all threads, this will not scale at
all, so there's no point in enabling thread-groups there. Modern
systems have epoll, kqueue or event ports and do not need these ones.
We arrange for failing at boot time, only when thread-groups > 1 so
that existing setups will remain unaffected.
If there's a compelling reason for supporting thread groups with these
pollers in the future, the rework should not be too hard, it would just
consume a lot of memory to have an fd_evts[] array per thread, but that
is doable.
When returning from the polling syscall, all pollers have a certain
dance to follow, made of wall clock updates, thread harmless updates,
idle time management and sleeping mask updates. Let's have a centralized
function to deal with all of this boring stuff: fd_leaving_poll(), and
make all the pollers use it.
Pollers are among the few remaining blocks still using constructors
to register themselves. That's not needed anymore since the initcalls
so better turn to initcalls.
Instead of fiddling with before_poll and after_poll in
activity_count_runtime(), the function is now called by
clock_entering_poll() which passes it the number of microseconds
spent working. This allows to remove all calls to
activity_count_runtime() from the pollers.
The entering_poll/leaving_poll/measure_idle functions that were hard
to classify and used to move to various locations have now been placed
into clock.c since it's precisely about time-keeping. The functions
were renamed to clock_*. The samp_time and idle_time values are now
static since there is no reason for them to be read from outside.
There is currently a problem related to time keeping. We're mixing
the functions to perform calculations with the os-dependent code
needed to retrieve and adjust the local time.
This patch extracts from time.{c,h} the parts that are solely dedicated
to time keeping. These are the "now" or "before_poll" variables for
example, as well as the various now_*() functions that make use of
gettimeofday() and clock_gettime() to retrieve the current time.
The "tv_*" functions moved there were also more appropriately renamed
to "clock_*".
Other parts used to compute stolen time are in other files, they will
have to be picked next.
time.h is a horrible place to put activity calculation, it's a
historical mistake because the functions were there. We already have
most of the parts in sched.{c,h} and these ones make an exception in
the middle, forcing time.h to include some thread stuff and to access
the before/after_poll and idle_pct values.
Let's move these 3 functions to task.h with the other ones. They were
prefixed with "sched_" instead of the historical "tv_" which already
made no sense anymore.
The current principle of running under isolation was made to access
sensitive data while being certain that no other thread was using them
in parallel, without necessarily having to place locks everywhere. The
main use case are "show sess" and "show fd" which run over long chains
of pointers.
The thread_isolate() call relies on the "harmless" bit that indicates
for a given thread that it's not currently doing such sensitive things,
which is advertised using thread_harmless_now() and which ends usings
thread_harmless_end(), which also waits for possibly concurrent threads
to complete their work if they took this opportunity for starting
something tricky.
As some system calls were notoriously slow (e.g. mmap()), a bunch of
thread_harmless_now() / thread_harmless_end() were placed around them
to let waiting threads do their work while such other threads were not
able to modify memory contents.
But this is not sufficient for performing memory modifications. One such
example is the server deletion code. By modifying memory, it not only
requires that other threads are not playing with it, but are not either
in the process of touching it. The fact that a pool_alloc() or pool_free()
on some structure may call thread_harmless_now() and let another thread
start to release the same object's memory is not acceptable.
This patch introduces the concept of "idle threads". Threads entering
the polling loop are idle, as well as those that are waiting for all
others to become idle via the new function thread_isolate_full(). Once
thread_isolate_full() is granted, the thread is not idle anymore, and
it is released using thread_release() just like regular isolation. Its
users have to keep in mind that across this call nothing is granted as
another thread might have performed shared memory modifications. But
such users are extremely rare and are actually expecting this from their
peers as well.
Note that that in case of backport, this patch depends on previous patch:
MINOR: threads: make thread_release() not wait for other ones to complete
This function already performs a number of checks prior to calling the
IOCB, and detects the change of thread (FD migration). Half of the
controls are still in each poller, and these pollers also maintain
activity counters for various cases.
Note that the unreliable test on thread_mask was removed so that only
the one performed by fd_set_running() is now used, since this one is
reliable.
Let's centralize all that fd-specific logic into the function and make
it return a status among:
FD_UPDT_DONE, // update done, nothing else to be done
FD_UPDT_DEAD, // FD was already dead, ignore it
FD_UPDT_CLOSED, // FD was closed
FD_UPDT_MIGRATED, // FD was migrated, ignore it now
Some pollers already used to call it last and have nothing to do after
it, regardless of the result. epoll has to delete the FD in case a
migration is detected. Overall this removes more code than it adds.
In 1.8, commit ab62f5195 ("MINOR: polling: Use fd_update_events to update
events seen for a fd") updated the pollers to rely on fd_update_events(),
but the modification delayed the test of presence of the FD in the report,
resulting in owner/thread_mask and possibly event updates being performed
for each FD appearing in a block of 32 FDs around an active one. This
caused the request rate to be ~3 times lower with select() than poll()
under 6 threads.
This can be backported as far as 1.8.
This patch replaces roughly all occurrences of an HA_ATOMIC_ADD(&foo, 1)
or HA_ATOMIC_SUB(&foo, 1) with the equivalent HA_ATOMIC_INC(&foo) and
HA_ATOMIC_DEC(&foo) respectively. These are 507 changes over 45 files.
This makes the code more readable and less prone to copy-paste errors.
In addition, it allows to place some __builtin_constant_p() predicates
to trigger a link-time error in case the compiler knows that the freed
area is constant. It will also produce compile-time error if trying to
free something that is not a regular pointer (e.g. a function).
The DEBUG_MEM_STATS macro now also defines an instance for ha_free()
so that all these calls can be checked.
178 occurrences were converted. The vast majority of them were handled
by the following Coccinelle script, some slightly refined to better deal
with "&*x" or with long lines:
@ rule @
expression E;
@@
- free(E);
- E = NULL;
+ ha_free(&E);
It was verified that the resulting code is the same, more or less a
handful of cases where the compiler optimized slightly differently
the temporary variable that holds the copy of the pointer.
A non-negligible amount of {free(str);str=NULL;str_len=0;} are still
present in the config part (mostly header names in proxies). These
ones should also be cleaned for the same reasons, and probably be
turned into ist strings.
When DEBUG_FD is set at build time, we'll keep a counter of per-FD events
in the fdtab. This counter is reported in "show fd" even for closed FDs if
not zero. The purpose is to help spot situations where an apparently closed
FD continues to be reported in loops, or where some events are dismissed.
We have poll_drop, poll_dead and poll_skip which are confusingly named
like their poll_io and poll_exp counterparts except that they are not
per poll() call but per-fd. This patch renames them to poll_drop_fd(),
poll_dead_fd() and poll_skip_fd() for this reason.
The "show activity" output mentions a number of indicators to explain
wake up reasons but doesn't have the number of times poll() sees some
I/O. And given that multiple events can happen simultaneously, it's
not always possible to deduce this metric by subtracting.
This patch adds a new "poll_io" counter that allows one to see how
often poll() returns with at least one active FD. This should help
detect stuck events and measure various ratios of poll sub-metrics.
This patch fixes all the leftovers from the include cleanup campaign. There
were not that many (~400 entries in ~150 files) but it was definitely worth
doing it as it revealed a few duplicates.
Since these are used as type attributes or conditional clauses, they
are used about everywhere and should not require a dependency on
thread.h. Moving them to compiler.h along with other similar statements
like ALIGN() etc looks more logical; this way they become part of the
base API. This allowed to remove thread-t.h from ~12 files, one was
found to only require thread-t and not thread and dict.c was found to
require thread.h.
global.h was one of the messiest files, it has accumulated tons of
implicit dependencies and declares many globals that make almost all
other file include it. It managed to silence a dependency loop between
server.h and proxy.h by being well placed to pre-define the required
structs, forcing struct proxy and struct server to be forward-declared
in a significant number of files.
It was split in to, one which is the global struct definition and the
few macros and flags, and the rest containing the functions prototypes.
The UNIX_MAX_PATH definition was moved to compat.h.
A few includes were missing in each file. A definition of
struct polled_mask was moved to fd-t.h. The MAX_POLLERS macro was
moved to defaults.h
Stdio used to be silently inherited from whatever path but it's needed
for list_pollers() which takes a FILE* and which can thus not be
forward-declared.
This moves types/activity.h to haproxy/activity-t.h and
proto/activity.h to haproxy/activity.h.
The macros defining the bit field values for the profiling variable
were moved to the type file to be more future-proof.
This one is included almost everywhere and used to rely on a few other
.h that are not needed (unistd, stdlib, standard.h). It could possibly
make sense to split it into multiple parts to distinguish operations
performed on timers and the internal time accounting, but at this point
it does not appear much important.
This splits the hathreads.h file into types+macros and functions. Given
that most users of this file used to include it only to get the definition
of THREAD_LOCAL and MAXTHREADS, the bare minimum was placed into thread-t.h
(i.e. types and macros).
All the thread management was left to haproxy/thread.h. It's worth noting
the drop of the trailing "s" in the name, to remove the permanent confusion
that arises between this one and the system implementation (no "s") and the
makefile's option (no "s").
For consistency, src/hathreads.c was also renamed thread.c.
A number of files were updated to only include thread-t which is the one
they really needed.
Some future improvements are possible like replacing empty inlined
functions with macros for the thread-less case, as building at -O0 disables
inlining and causes these ones to be emitted. But this really is cosmetic.
All files that were including one of the following include files have
been updated to only include haproxy/api.h or haproxy/api-t.h once instead:
- common/config.h
- common/compat.h
- common/compiler.h
- common/defaults.h
- common/initcall.h
- common/tools.h
The choice is simple: if the file only requires type definitions, it includes
api-t.h, otherwise it includes the full api.h.
In addition, in these files, explicit includes for inttypes.h and limits.h
were dropped since these are now covered by api.h and api-t.h.
No other change was performed, given that this patch is large and
affects 201 files. At least one (tools.h) was already freestanding and
didn't get the new one added.
Commit 42a50bd19 ("BUG/MINOR: pollers: remove uneeded free in global
init") removed the 'fail_revt' label from the _do_init() function
in src/ev_select.c but left the local label declaration, which makes
clang unhappy and unable to build.
These labels are only historic and unneeded anyway so let's remove them.
This should be backported where 42a50bd19 is backported.
while reading the code, I thought it was clearer to put one instruction
per line as it is mostly done elsewhere
Signed-off-by: William Dauchy <w.dauchy@criteo.com>
Since commit d4604adeaa ("MAJOR: threads/fd: Make fd stuffs
thread-safe"), we init pollers per thread using a helper. It was still
correct for mono-thread mode until commit cd7879adc2 ("BUG/MEDIUM:
threads: Run the poll loop on the main thread too"). We now use a deinit
helper for all threads, making those free uneeded.
Only poll and select are affected by this very minor issue.
it could be backported from v1.8 to v2.1.
Fixes: cd7879adc2 ("BUG/MEDIUM: threads: Run the poll loop on the main
thread too")
Signed-off-by: William Dauchy <w.dauchy@criteo.com>
This used to be a minor optimization on ix86 where registers are scarce
and the calling convention not very efficient, but this platform is not
relevant enough anymore to warrant all this dirt in the code for the sake
of saving 1 or 2% of performance. Modern platforms don't use this at all
since their calling convention already defaults to using several registers
so better get rid of this once for all.
As mentioned in previous commit, these flags do not map well to
modern poller capabilities. Let's use the FD_EV_*_{R,W} flags instead.
This first patch only performs a 1-to-1 mapping making sure that the
previously reported flags are still reported identically while using
the closest possible semantics in the pollers.
It's worth noting that kqueue will now support improvements such as
returning distinctions between shut and errors on each direction,
though this is not exploited for now.
Since commit 7ac0e35f2 in 1.9-dev1 ("MAJOR: fd: compute the new fd polling
state out of the fd lock") we've started to update the FD POLLED bit a
bit more aggressively. Lately with the removal of the FD cache, this bit
is always equal to the ACTIVE bit. There's no point continuing to watch
it and update it anymore, all it does is create confusion and complicate
the code. One interesting side effect is that it now becomes visible that
all fd_*_{send,recv}() operations systematically call updt_fd_polling(),
except fd_cant_recv()/fd_cant_send() which never saw it change.
In _update_fd(), if we're about to remove the FD from the poller, remove
both the receive and the send bits, instead of removing the receive bits
twice.
In the poller code, instead of just remembering if we're currently polling
a fd or not, remember if we're polling it for writing and/or for reading, that
way, we can avoid to modify the polling if it's already polled as needed.
Now that the architecture was changed so that attempts to receive/send data
always come from the upper layers, instead of them only trying to do so when
the lower layer let them know they could try, we can finally get rid of the
fd cache. We don't really need it anymore, and removing it gives us a small
performance boost.
We have been abusing the do_poll()'s timeout for a while, making it zero
whenever there is some known activity. The problem this poses is that it
complicates activity diagnostic by incrementing the poll_exp field for
each known activity. It also requires extra computations that could be
avoided.
This change passes a "wake" argument to say that the poller must not
sleep. This simplifies the operations and allows one to differenciate
expirations from activity.
At the moment the situation with activity measurement is quite tricky
because the struct activity is defined in global.h and declared in
haproxy.c, with operations made in time.h and relying on freq_ctr
which are defined in freq_ctr.h which itself includes time.h. It's
barely possible to touch any of these files without breaking all the
circular dependency.
Let's move all this stuff to activity.{c,h} and be done with it. The
measurement of active and stolen time is now done in a dedicated
function called just after tv_before_poll() instead of mixing the two,
which used to be a lazy (but convenient) decision.
No code was changed, stuff was just moved around.
By placing this code into time.h (tv_entering_poll() and tv_leaving_poll())
we can remove the logic from the pollers and prepare for extending this to
offer more accurate time measurements.
The 4 pollers all contain the same code used to compute the poll timeout.
This is pointless, let's centralize this into fd.h. This also gets rid of
the useless SCHEDULER_RESOLUTION macro which used to work arond a very old
linux 2.2 bug causing select() to wake up slightly before the timeout.
The current synchronization point enforces certain restrictions which
are hard to workaround in certain areas of the code. The fact that the
critical code can only be called from the sync point itself is a problem
for some callback-driven parts. The "show fd" command for example is
fragile regarding this.
Also it is expensive in terms of CPU usage because it wakes every other
thread just to be sure all of them join to the rendez-vous point. It's a
problem because the sleeping threads would not need to be woken up just
to know they're doing nothing.
Here we implement a different approach. We keep track of harmless threads,
which are defined as those either doing nothing, or doing harmless things.
The rendez-vous is used "for others" as a way for a thread to isolate itself.
A thread then requests to be alone using thread_isolate() when approaching
the dangerous area, and then waits until all other threads are either doing
the same or are doing something harmless (typically polling). The function
only returns once the thread is guaranteed to be alone, and the critical
section is terminated using thread_release().
The polled_mask is only used in the pollers, and removing it from the
struct fdtab makes it fit in one 64B cacheline again, on a 64bits machine,
so make it a separate array.
With the old model, any fd shared by multiple threads, such as listeners
or dns sockets, would only be updated on one threads, so that could lead
to missed event, or spurious wakeups.
To avoid this, add a global list for fd that are shared, using the same
implementation as the fd cache, and only remove entries from this list
when every thread as updated its poller.
[wt: this will need to be backported to 1.8 but differently so this patch
must not be backported as-is]
Clearing the update_mask bit in fd_insert may lead to duplicate insertion
of fd in fd_updt, that could lead to a write past the end of the array.
Instead, make sure the update_mask bit is cleared by the pollers no matter
what.
This should be backported to 1.8.
[wt: warning: 1.8 doesn't have the lockless fdcache changes and will
require some careful changes in the pollers]
