Previous implementation would use a random factor to spread readers and
reduce chances of starvation. This visibly reduces effectiveness of the
mechanism.
Switch to the more traditional exponential variant. Try to limit starvation
by imposing an upper limit of spins after which spinning is half of what
other threads get. Note the mechanism is turned off by default.
Reviewed by: kib (previous version)
reasons. First is rerooting into USB-mounted device that happens
to be not yet enumerated. The second is when mounting with (non-root)
filesystem on USB device on a hub that's enumerated later than the root
mount: the rc scripts explicitly mount for the root mount holds to be
released, but each USB bus takes the hold asynchronously, and if that
happens after root mount, it would just get ignored.
Reviewed by: marcel
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9388
for mount hold release if the root device already exists. So, unless your
rootdev is not on USB - ie in the usual case - the root mount won't wait
for USB. However, the old behaviour was sometimes used as "wait until USB
is fully enumerated", and r290196 broke that.
This commit adds vfs.root_mount_always_wait tunable, to force the kernel
to always wait for root mount holds, even if the root is already there.
Reviewed by: kib
MFC after: 2 weeks
Relnotes: yes
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9387
controller drivers handle either MSI/MSI-X interrupts, or regular
interrupts, as such enforce this in the interrupt handling framework.
If a later driver was to handle both it would need to create one of each.
This will allow future changes to allow the xref space to overlap, but
refer to different drivers.
Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation
X-Differential Revision: https://reviews.freebsd.org/D8616
When a relevant lockstat probe is enabled the fallback primitive is called with
a constant signifying a free lock. This works fine for typical cases but breaks
with recursion, since it checks if the passed value is that of the executing
thread.
Read the value if necessary.
See r313275 for details.
One difference here is that recursion handling was removed from the fallback
routine. As it is it was never supposed to see a recursed lock in the first
place. Future changes will move it out of inline variants, but right now
there is no easy to way to test if the lock is recursed without reading
additional words.
and use it in compats instead of their sys_*() counterparts.
Reviewed by: kib, jhb, dchagin
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9383
Lockstat requires checking if it is enabled and if so, calling a 6 argument
function. Further, determining whether to call it on unlock requires
pre-reading the lock value.
This is problematic in at least 3 ways:
- more branches in the hot path than necessary
- additional cacheline ping pong under contention
- bigger code
Instead, check first if lockstat handling is necessary and if so, just fall
back to regular locking routines. For this purpose a new macro is introduced
(LOCKSTAT_PROFILE_ENABLED).
LOCK_PROFILING uninlines all primitives. Fold in the current inline lock
variant into the _mtx_lock_flags to retain the support. With this change
the inline variants are not used when LOCK_PROFILING is defined and thus
can ignore its existence.
This results in:
text data bss dec hex filename
22259667 1303208 4994976 28557851 1b3c21b kernel.orig
21797315 1303208 4994976 28095499 1acb40b kernel.patched
i.e. about 3% reduction in text size.
A remaining action is to remove spurious arguments for internal kernel
consumers.
Shared locking routines explicitly read the value and test it. If the
change attempt fails, they fall back to a regular function which would
retry in a loop.
The problem is that with many concurrent readers the risk of failure is pretty
high and even the value returned by fcmpset is very likely going to be stale
by the time the loop in the fallback routine is reached.
Uninline said primitives. It gives a throughput increase when doing concurrent
slocks/sunlocks with 80 hardware threads from ~50 mln/s to ~56 mln/s.
Interestingly, rwlock primitives are already not inlined.
The found value is passed to locking routines in order to reduce cacheline
accesses.
mtx_unlock grows an explicit check for regular unlock. On ll/sc architectures
the routine can fail even if the lock could have been handled by the inline
primitive.
Discussed with: jhb
Tested by: pho (previous version)
witness_warn() either breaks into the debugger or panics the system, so its
output should go to the console regardless of the witness(4) output channel
configuration.
MFC after: 1 week
Sponsored by: Dell EMC Isilon
The switch to get_pcpu() in MI code seems to cause hangs on MIPS.
Back out until we can get a better idea of what's happening there.
Reported by: kan, lidl
for EVFILT_READ at the point of the check not when the event is registers.
This fixes a problem with asio when accepting a connection.
Reviewed by: kib@, Scott Mitchell
of their sys_*() counterparts. The svr4 is left unchanged.
Reviewed by: kib@
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9379
The checks have quadratic complexity over a number of advisory locks
active for a file and that could be a lot. What's the worse is that the
checks are done while holding ls_lock. That could lead to a long a very
long backlog and performance degradation even if all requested locks are
compatible (e.g. all shared locks).
The checks used to be under INVARIANTS.
Discussed with: kib
MFC after: 2 weeks
Sponsored by: Panzura
instead of their sys_*() counterparts in various compats. The svr4
is left untouched, because there's no point.
Reviewed by: ed@, kib@
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9367
Add additionally safety and overflow checks to clock_ts_to_ct and the
BCD routines while we're here.
Perform a safety check in sys_clock_settime() first to avoid easy local
root panic, without having to propagate an error value back through
dozens of APIs currently lacking error returns.
PR: 211960, 214300
Submitted by: Justin McOmie <justin.mcomie at gmail.com>, kib@
Reported by: Tim Newsham <tim.newsham at nccgroup.trust>
Reviewed by: kib@
Sponsored by: Dell EMC Isilon, FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D9279
Add internal tracking of smp startup status to reliably figure out
what methods are to be used to get gtaskqueue up and running.
e1000:
Calculating this pointer gives undefined behaviour when (last == -1)
(it is before the buffer). The pointer is always followed. Panics
occurred when it points to an unmapped page. Otherwise, the pointed-to
garbage tends to not have the E1000_TXD_STAT_DD bit set in it, so in the
broken case the loop was usually null and the function just returned, and
this was acidentally correct.
Submitted by: bde
Reported by: Matt Macy <mmacy@nextbsd.org>
