This patch looks huge, but it has a very simple goal: protect all
accessed to shared stats pointers (either read or writes), because
we know consider that these pointers may be NULL.
The reason behind this is despite all precautions taken to ensure the
pointers shouldn't be NULL when not expected, there are still corner
cases (ie: frontends stats used on a backend which no FE cap and vice
versa) where we could try to access a memory area which is not
allocated. Willy stumbled on such cases while playing with the rings
servers upon connection error, which eventually led to process crashes
(since 3.3 when shared stats were implemented)
Also, we may decide later that shared stats are optional and should
be disabled on the proxy to save memory and CPU, and this patch is
a step further towards that goal.
So in essence, this patch ensures shared stats pointers are always
initialized (including NULL), and adds necessary guards before shared
stats pointers are de-referenced. Since we already had some checks
for backends and listeners stats, and the pointer address retrieval
should stay in cpu cache, let's hope that this patch doesn't impact
stats performance much.
The current guid struct size is 56 bytes. Once reduced using compact
trees, it goes down to 32 (almost half). We're not on a critical path
and size matters here, so better switch to this.
It's worth noting that the name part could also be stored in the
guid_node at the end to save 8 extra byte (no pointer needed anymore),
however the purpose of this struct is to be embedded into other ones,
which is not compatible with having a dynamic size.
Affected struct sizes in bytes:
Before After Diff
server 4032 4032 0*
proxy 3184 3160 -24
listener 752 728 -24
*: struct server is full of holes and padding (176 bytes) and is
64-byte aligned. Moving the guid_node elsewhere such as after sess_conn
reduces it to 3968, or one less cache line. There's no point in moving
anything now because forthcoming patches will arrange other parts.
As reported in GH #3104, there remained a place where (1 << shift was
used to set or remove bits from uint64_t users bitfield. It is incorrect
and could lead to bugs for values > 32 bits.
Instead, let's use 1ULL to ensure the operation remains 64bits consistent.
No backport needed.
Add two BUG_ON() in shm_stats_file_prepare() which will trigger if
exported structures (shm_stats_file_hdr and shm_stats_file_object) change
in size, because it means that they will become incompatible with older
versions and thus precautions should be taken by the developer to ensure
compatibility with olders versions, or at least detect incompatible
versions by changing the version number to prevent bugs resulting
from inconsistent mapping between versions. The BUG_ON() may be
safely adjusted then.
Please note that it doesn't protect against accidental struct member
re-ordering if the resulting struct size is equal..
shm_stats_file_reuse_object() has a non negligible cost, especially if
the shm file contains a lot of objects because the functions scans the
whole shm file to find available slots.
During startup, if no existing objects could be mapped in the shm
file shm_stats_file_add_object() for each object (server, fe, be or
listener) with a GUID set. On large config it means
shm_stats_file_add_object() could be called a lot of times in a row.
With current implementation, each shm_stats_file_add_object() call
leverages shm_stats_file_reuse_object(), so the more objects are defined
in the config, the slower the startup will be.
To try to optimize startup time a bit with large configs, we don't
sytematically call shm_stats_file_reuse_object(), especially when we
know that the previous attempt to reuse objects failed. In this case
we add a small tempo between failed attempts to reuse objects because
we assume the new attempt will probably fail anyway. (For slots to
become available, either an old process has to clean its entries,
or they have to time out which implies that the clock needs to be updated)
This is the last patch of the shm stats file series, in this patch we
implement the logic to store and fetch shm stats objects and associate
them to existing shared counters on the current process.
Shm objects are stored in the same memory location as the shm stats file
header. In fact they are stored right after it. All objects (struct
shm_stats_file_object) have the same size (no matter their type), which
allows for easy object traversal without having to check the object's
type, and could permit the use of external tools to scan the SHM in the
future. Each object stores a guid (of GUID_MAX_LEN+1 size) and tgid
which allows to match corresponding shared counters indexes. Also,
as stated before, each object stores the list of users making use of
it. Objects are never released (the map can only grow), but unused
objects (when no more users or active users are found in objects->users),
the object is automatically recycled. Also, each object stores its
type which defines how the object generic data member should be handled.
Upon startup (or reload), haproxy first tries to scan existing shm to
find objects that could be associated to frontends, backends, listeners
or servers in the current config based on GUID. For associations that
couldn't be made, haproxy will automatically create missing objects in
the SHM during late startup. When haproxy matches with an existing object,
it means the counter from an older process is preserved in the new
process, so multiple processes temporarily share the same counter for as
long as required for older processes to eventually exit.
Now that all processes tied to the same shm stats file now share a
common clock source, we introduce the process slot notion in this
patch.
Each living process registers itself in a map at a free index: each slot
stores information about the process' PID and heartbeat. Each process is
responsible for updating its heartbeat, a slot is considered as "free" if
the heartbeat was never set or if the heartbeat is expired (60 seconds of
inactivity). The total number of slots is set to 64, this is on purpose
because it allows to easily store the "users" of a given shm object using
a 64 bits bitmask. Given that when haproxy is reloaded olders processes
are supposed to die eventually, it should be large enough (64 simultaneous
processes) to be safe. If we manage to reach this limit someday, more
slots could be added by splitting "users" bitmask on multiple 64bits
variable.
The use of the "shm-stats-file" directive now implies that all processes
using the same file now share a common clock source, this is required
for consistency regarding time-related operations.
The clock source is stored in the shm stats file header.
When the directive is set, all processes share the same clock
(global_now_ms and global_now_ns both point to variables in the map),
this is required for time-based counters such as freq counters to work
consistently. Since all processes manipulate global clock with atomic
operations exclusively during runtime, and don't systematically relies
on it (thanks to local now_ms and now_ns), it is pretty much transparent.
add initial support for the "shm-stats-file" directive and
associated "shm-stats-file-max-objects" directive. For now they are
flagged as experimental directives.
The shared memory file is automatically created by the first process.
The file is created using open() so it is up to the user to provide
relevant path (either on regular filesystem or ramfs for performance
reasons). The directive takes only one argument which is path of the
shared memory file. It is passed as-is to open().
The maximum number of objects per thread-group (hard limit) that can be
stored in the shm is defined by "shm-stats-file-max-objects" directive,
Upon initial creation, the main shm stats file header is provisioned with
the version which must remains the same to be compatible between processes
and defaults to 2k. which means approximately 1mb max per thread group
and should cover most setups. When the limit is reached (during startup)
an error is reported by haproxy which invites the user to increase the
"shm-stats-file-max-objects" if desired, but this means more memory will
be allocated. Actual memory usage is low at start, because only the mmap
(mapping) is provisionned with the maximum number of objects to avoid
relocating the memory area during runtime, but the actual shared memory
file is dynamically resized when objects are added (resized by following
half power of 2 curve when new objects are added, see upcoming commits)
For now only the file is created, further logic will be implemented in
upcoming commits.
Between 3.2 and 3.3-dev we noticed a noticeable performance regression
due to stats handling. After bisecting, Willy found out that recent
work to split stats computing accross multiple thread groups (stats
sharding) was responsible for that performance regression. We're looking
at roughly 20% performance loss.
More precisely, it is the added indirections, multiplied by the number
of statistics that are updated for each request, which in the end causes
a significant amount of time being spent resolving pointers.
We noticed that the fe_counters_shared and be_counters_shared structures
which are currently allocated in dedicated memory since a0dcab5c
("MAJOR: counters: add shared counters base infrastructure")
are no longer huge since 16eb0fab31 ("MAJOR: counters: dispatch counters
over thread groups") because they now essentially hold flags plus the
per-thread group id pointer mapping, not the counters themselves.
As such we decided to try merging fe_counters_shared and
be_counters_shared in their parent structures. The cost is slight memory
overhead for the parent structure, but it allows to get rid of one
pointer indirection. This patch alone yields visible performance gains
and almost restores 3.2 stats performance.
counters_fe_shared_get() was renamed to counters_fe_shared_prepare() and
now returns either failure or success instead of a pointer because we
don't need to retrieve a shared pointer anymore, the function takes care
of initializing existing pointer.
Most fe and be counters are good candidates for being shared between
processes. They are now grouped inside "shared" struct sub member under
be_counters and fe_counters.
Now they are properly identified, they would greatly benefit from being
shared over thread groups to reduce the cost of atomic operations when
updating them. For this, we take the current tgid into account so each
thread group only updates its own counters. For this to work, it is
mandatory that the "shared" member from {fe,be}_counters is initialized
AFTER global.nbtgroups is known, because each shared counter causes the stat
to be allocated lobal.nbtgroups times. When updating a counter without
concurrency, the first counter from the array may be updated.
To consult the shared counters (which requires aggregation of per-tgid
individual counters), some helper functions were added to counter.h to
ease code maintenance and avoid computing errors.
Shareable counters are not tagged as shared counters and are dynamically
allocated in separate memory area as a prerequisite for being stored
in shared memory area. For now, GUID and threads groups are not taken into
account, this is only a first step.
also we ensure all counters are now manipulated using atomic operations,
namely, "last_change" counter is now read from and written to using atomic
ops.
Despite the numerous changes caused by the counters being moved away from
counters struct, no change of behavior should be expected.
Most of the invalid or unknow field in the stats-file parser are ignored
silently, which is not the case of the frontend/backend mismatch on a
guid, which is kind of strange.
Since this is ""documented"" to be ignored in the
reg-tests/stats/sample-stats-file file, let's also ignore this kind of
line. This will allow to run the associated reg-test with -dW.
getline() was used to read stats-file. However, this function is not
portable and may cause build issue on some systems. Replace it by
standard fgets().
No need to backport.
Extend generic stat column support to be able to fully support age stats
type. Several changes were required.
On output, me_generate_field() has been updated to report the difference
between the current tick with the stored value for FN_AGE type. Also, if
an age stats is hidden in show stats, -1 is returned instead of an empty
metric, which is the value to mark an age as unset.
On counters preload, load_ctr() was updated to handled FN_AGE. A similar
substraction is performed to the current tick value.
Implement support for FN_RATE stat column into stat-file.
For the output part, only minimal change is required. Reuse the function
read_freq_ctr() to print the same value in both stats output and
stats-file dump.
For counter preloading, define a new utility function
preload_freq_ctr(). This can be used to initialize a freq-ctr type by
preloading previous period value. Reuse this function in load_ctr()
during stats-file parsing.
At the moment, no rate column is defined as generic. Thus, this commit
does not have functional change. This will be changed as soon as FN_RATE
are converted to generic columns.
Currently, only FN_COUNTER are dumped and preloaded via a stats-file.
Thus in several places we relied on the assumption that only FN_COUNTER
are valid in stats-file context.
New stats types will soon be implemented as they are also eligilible to
statistics reloading on process startup. Thus, prepare stats-file
functions to remove any FN_COUNTER restriction.
As one of this change, generate_stat_tree() now uses stcol_is_generic()
for stats name tree indexing before stats-file parsing.
Also related to stats-file parsing, individual counter preloading step
as been extracted from line parsing in a dedicated new function
load_ctr(). This will allow to extend it to support multiple mechanism
of counter preloading depending on the stats type.
Update parse_stat_line() used during stats-file parsing. For each line,
GUID is extracted first to access to the object instance. obj_type()
is then invoked to retrieve the correct object type.
Replace objt_* by __objt_* macros to mark its result as safe and non
NULL.
This should fix coverity report from github issue #2550.
No need to backport.
This patch implement parsing of counter values line from stats-file. It
reuses domain context previously set by the last header line. Each
value is separated by ',' character, relative to the list of column
names describe by the header line.
This is implemented via static function parse_stat_line(). It first
extract a GUID and retrieve the object instance. Then each numerical
value is parsed and object counters updated. For the moment, only U64
counters metrics is supported. parse_stat_line() is called on each line
until a new header line is found.
This patch implements parsing of headers line from stats-file.
A header line is defined as starting with '#' character. It is directly
followed by a domain name. For the moment, either 'fe' or 'be' is
allowed. The following lines will contain counters values relatives to
the domain context until the next header line.
This is implemented via static function parse_header_line(). It first
sets the domain context used during apply_stats_file(). A stats column
array is generated to contains the order on which column are stored.
This will be reused to parse following lines values.
If an invalid line is found and no header was parsed, considered the
stats-file as ill formatted and stop parsing. This allows to immediately
interrupt parsing if a garbage file was used without emitting a ton of
warnings to the user.
This commit is the first one of a serie to implement preloading of
haproxy counters via stats-file parsing.
This patch defines a basic apply_stats_file() function. It implements
reading line by line of a stats-file without any parsing for the moment.
It is called automatically on process startup via init().
Define a new CLI command "dump stats-file" with its handler
cli_parse_dump_stat_file(). It will loop twice on proxies_list to dump
first frontend and then backend side. It reuses the common function
stats_dump_stat_to_buffer(), using STAT_F_BOUND to restrict on the
correct side.
A new module stats-file.c is added to regroup function specifics to
stats-file. It defines two main functions :
* stats_dump_file_header() to generate the list of column list prefixed
by the line context, either "#fe" or "#be"
* stats_dump_fields_file() to generate each stat lines. Object without
GUID are skipped. Each stat entry is separated by a comma.
For the moment, stats-file does not support statistics modules. As such,
stats_dump_*_line() functions are updated to prevent looping over stats
module on stats-file output.
