turnstile_{lock,unlock}() were added for use in epoch. turnstile_lock()
returned NULL to indicate that the calling thread had lost a race and
the turnstile was no longer associated with the given lock, or the lock
owner. However, reader-writer locks may not have a designated owner,
in which case turnstile_lock() would return NULL and
epoch_block_handler_preempt() would leak spinlocks as a result.
Apply a minimal fix: return the lock owner as a separate return value.
Reviewed by: kib
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D21048
The epoch_drain_callbacks() function is used to drain all pending
callbacks which have been invoked by prior epoch_call() function calls
on the same epoch. This function is useful when there are shared
memory structure(s) referred to by the epoch callback(s) which are not
refcounted and are rarely freed. The typical place for calling this
function is right before freeing or invalidating the shared
resource(s) used by the epoch callback(s). This function can sleep and
is not optimized for performance.
Differential Revision: https://reviews.freebsd.org/D20109
MFC after: 1 week
Sponsored by: Mellanox Technologies
So far, intr_{g,s}etaffinity(9) take a single int for identifying
a device interrupt. This approach doesn't work on all architectures
supported, as a single int isn't sufficient to globally specify a
device interrupt. In particular, with multiple interrupt controllers
in one system as found on e. g. arm and arm64 machines, an interrupt
number as returned by rman_get_start(9) may be only unique relative
to the bus and, thus, interrupt controller, a certain device hangs
off from.
In turn, this makes taskqgroup_attach{,_cpu}(9) and - internal to
the gtaskqueue implementation - taskqgroup_attach_deferred{,_cpu}()
not work across architectures. Yet in turn, iflib(4) as gtaskqueue
consumer so far doesn't fit architectures where interrupt numbers
aren't globally unique.
However, at least for intr_setaffinity(..., CPU_WHICH_IRQ, ...) as
employed by the gtaskqueue implementation to bind an interrupt to a
particular CPU, using bus_bind_intr(9) instead is equivalent from
a functional point of view, with bus_bind_intr(9) taking the device
and interrupt resource arguments required for uniquely specifying a
device interrupt.
Thus, change the gtaskqueue implementation to employ bus_bind_intr(9)
instead and intr_{g,s}etaffinity(9) to take the device and interrupt
resource arguments required respectively. This change also moves
struct grouptask from <sys/_task.h> to <sys/gtaskqueue.h> and wraps
struct gtask along with the gtask_fn_t typedef into #ifdef _KERNEL
as userland likes to include <sys/_task.h> or indirectly drags it
in - for better or worse also with _KERNEL defined -, which with
device_t and struct resource dependencies otherwise is no longer
as easily possible now.
The userland inclusion problem probably can be improved a bit by
introducing a _WANT_TASK (as well as a _WANT_MOUNT) akin to the
existing _WANT_PRISON etc., which is orthogonal to this change,
though, and likely needs an exp-run.
While at it:
- Change the gt_cpu member in the grouptask structure to be of type
int as used elswhere for specifying CPUs (an int16_t may be too
narrow sooner or later),
- move the gtaskqueue_enqueue_fn typedef from <sys/gtaskqueue.h> to
the gtaskqueue implementation as it's only used and needed there,
- change the GTASK_INIT macro to use "gtask" rather than "task" as
argument given that it actually operates on a struct gtask rather
than a struct task, and
- let subr_gtaskqueue.c consistently use __func__ to print functions
names.
Reported by: mmel
Reviewed by: mmel
Differential Revision: https://reviews.freebsd.org/D19139
mutexes but now are converted to epoch(9) use thread-private epoch_tracker.
Embedding tracker into ifnet(9) or ifnet derived structures creates a non
reentrable function, that will fail miserably if called simultaneously from
two different contexts.
A thread private tracker will provide a single tracker that would allow to
call these functions safely. It doesn't allow nested call, but this is not
expected from compatibility KPIs.
Reviewed by: markj
processors would benefit from avoiding a function call, but bloating
code. In fact, clang created an uninlined real function for many
object files in the network stack.
- Move epoch_private.h into subr_epoch.c. Code copied exactly, avoiding
any changes, including style(9).
- Remove private copies of critical_enter/exit.
Reviewed by: kib, jtl
Differential Revision: https://reviews.freebsd.org/D17879
In discussing D17503 "Run epoch calls sooner and more reliably" with
sbahra@ we came to the conclusion that epoch is currently misusing the
ck_epoch API. It isn't safe to do a "write side" operation (ck_epoch_call
or ck_epoch_poll) in the middle of a "read side" section. Since, by definition,
it's possible to be preempted during the middle of an EPOCH_PREEMPT
epoch the GC task might call ck_epoch_poll or another thread might call
ck_epoch_call on the same section. The right solution is ultimately to change
the way that ck_epoch works for this use case. However, as a stopgap for
12 we agreed to simply have separate records for each use case.
Tested by: pho@
MFC after: 3 days
- Add tracker argument to preemptible epochs
- Inline epoch read path in kernel and tied modules
- Change in_epoch to take an epoch as argument
- Simplify tfb_tcp_do_segment to not take a ti_locked argument,
there's no longer any benefit to dropping the pcbinfo lock
and trying to do so just adds an error prone branchfest to
these functions
- Remove cases of same function recursion on the epoch as
recursing is no longer free.
- Remove the the TAILQ_ENTRY and epoch_section from struct
thread as the tracker field is now stack or heap allocated
as appropriate.
Tested by: pho and Limelight Networks
Reviewed by: kbowling at llnw dot com
Sponsored by: Limelight Networks
Differential Revision: https://reviews.freebsd.org/D16066
If EARLY_AP_STARTUP is not defined it is possible for an epoch to be
allocated prior to it being possible to call epoch_call without
issue.
Based on patch by andrew@
PR: 229014
Reported by: andrew
They're only useful when multiple threads may share an epoch record,
and that can't happen with non-preemptible sections.
Reviewed by: mmacy
Differential Revision: https://reviews.freebsd.org/D15507
There are risks associated with waiting on a preemptible epoch section.
Change the name to make them not be the default and document the issue
under CAVEATS.
Reported by: markj
adds:
- epoch_enter_critical() - can be called inside a different epoch,
starts a section that will acquire any MTX_DEF mutexes or do
anything that might sleep.
- epoch_exit_critical() - corresponding exit call
- epoch_wait_critical() - wait variant that is guaranteed that any
threads in a section are running.
- epoch_global_critical - an epoch_wait_critical safe epoch instance
Requested by: markj
Approved by: sbruno
Add epoch section to struct thread. We can use this to
ennable epoch counter to advance even if a section is
perpetually occupied by a thread.
Approved by: sbruno
The INVARIANTS checks in epoch_wait() were intended to
prevent the block handler from returning with locks held.
What it in fact did was preventing anything except Giant
from being held across it. Check that the number of locks
held has not changed instead.
Approved by: sbruno@
- GC the _nopreempt routines
- to really benefit we'd need a separate routine
- they're not currently in use
- they complicate the API for no benefit at this time
- check that we're actually in a epoch section at exit
- handle epoch_call() early in boot
- Fix copyright declaration language
Approved by: sbruno@
It appears that domain information is set correctly independent
of whether or not NUMA is defined. However, there is no memory
backing secondary domains leading to allocation failure.
Reported by: pho@, np@
Approved by: sbruno@
- initialize the pcpu STAILQ in the NUMA case
- don't enqueue the callback task if there isn't sufficient work to be done
Reported by: pho@
Approved by: sbruno@
- Lend priority to preempted threads in epoch_wait to handle the case
in which we've had priority lent to us. Previously we borrowed the
priority of the lowest priority preempted thread. (pointed out by mjg@)
- Don't attempt allocate memory per-domain on powerpc, we don't currently
handle empty sockets (as is the case on jhibbits Talos' board).
- Handle deferred callbacks as pcpu lists and poll the lists periodically.
Currently the interval is 1/hz.
- Drop the thread lock when adaptive spinning. Holding the lock starves
other threads and can even lead to lockups.
- Keep a generation count pcpu so that we don't keep spining if a thread
has left and re-entered an epoch section.
- Actually removed the callback from the callback list so that we don't
double free. Sigh ...
Approved by: sbruno@
Read locking is over used in the kernel to guarantee liveness. This API makes
it easy to provide livenes guarantees without atomics.
Includes epoch_test kernel module to stress test the API.
Documentation will follow initial use case.
Test case and improvements to preemption handling in response to discussion
with mjg@
Reviewed by: imp@, shurd@
Approved by: sbruno@
