31 May, 2019
1 commit
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Based on 3 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more detailsthis program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version [author] [kishon] [vijay] [abraham]
[i] [kishon]@[ti] [com] this program is distributed in the hope that
it will be useful but without any warranty without even the implied
warranty of merchantability or fitness for a particular purpose see
the gnu general public license for more detailsthis program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version [author] [graeme] [gregory]
[gg]@[slimlogic] [co] [uk] [author] [kishon] [vijay] [abraham] [i]
[kishon]@[ti] [com] [based] [on] [twl6030]_[usb] [c] [author] [hema]
[hk] [hemahk]@[ti] [com] this program is distributed in the hope
that it will be useful but without any warranty without even the
implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more detailsextracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 1105 file(s).
Signed-off-by: Thomas Gleixner
Reviewed-by: Allison Randal
Reviewed-by: Richard Fontana
Reviewed-by: Kate Stewart
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070033.202006027@linutronix.de
Signed-off-by: Greg Kroah-Hartman
02 Oct, 2018
1 commit
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Both spin locks and write locks currently do:
f0 0f b1 17 lock cmpxchg %edx,(%rdi)
85 c0 test %eax,%eax
75 05 jne [slowpath]This 'test' insn is superfluous; the cmpxchg insn sets the Z flag
appropriately. Peter pointed out that using atomic_try_cmpxchg_acquire()
will let the compiler know this is true. Comparing before/after
disassemblies show the only effect is to remove this insn.Take this opportunity to make the spin & write lock code resemble each
other more closely and have similar likely() hints.Suggested-by: Peter Zijlstra
Signed-off-by: Matthew Wilcox
Signed-off-by: Peter Zijlstra (Intel)
Acked-by: Will Deacon
Cc: Arnd Bergmann
Cc: Linus Torvalds
Cc: Thomas Gleixner
Cc: Waiman Long
Link: http://lkml.kernel.org/r/20180820162639.GC25153@bombadil.infradead.org
Signed-off-by: Ingo Molnar
25 Oct, 2017
3 commits
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When a prospective writer takes the qrwlock locking slowpath due to the
lock being held, it attempts to cmpxchg the wmode field from 0 to
_QW_WAITING so that concurrent lockers also take the slowpath and queue
on the spinlock accordingly, allowing the lockers to drain.Unfortunately, this isn't fair, because a fastpath writer that comes in
after the lock is made available but before the _QW_WAITING flag is set
can effectively jump the queue. If there is a steady stream of prospective
writers, then the waiter will be held off indefinitely.This patch restores fairness by separating _QW_WAITING and _QW_LOCKED
into two distinct fields: _QW_LOCKED continues to occupy the bottom byte
of the lockword so that it can be cleared unconditionally when unlocking,
but _QW_WAITING now occupies what used to be the bottom bit of the reader
count. This then forces the slow-path for concurrent lockers.Tested-by: Waiman Long
Tested-by: Jeremy Linton
Tested-by: Adam Wallis
Tested-by: Jan Glauber
Signed-off-by: Will Deacon
Acked-by: Peter Zijlstra
Cc: Boqun Feng
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Thomas Gleixner
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-6-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar -
The qrwlock slowpaths involve spinning when either a prospective reader
is waiting for a concurrent writer to drain, or a prospective writer is
waiting for concurrent readers to drain. In both of these situations,
atomic_cond_read_acquire() can be used to avoid busy-waiting and make use
of any backoff functionality provided by the architecture.This patch replaces the open-code loops and rspin_until_writer_unlock()
implementation with atomic_cond_read_acquire(). The write mode transition
zero to _QW_WAITING is left alone, since (a) this doesn't need acquire
semantics and (b) should be fast.Tested-by: Waiman Long
Tested-by: Jeremy Linton
Tested-by: Adam Wallis
Tested-by: Jan Glauber
Signed-off-by: Will Deacon
Acked-by: Peter Zijlstra
Cc: Boqun Feng
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Thomas Gleixner
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar -
There's no good reason to keep the internal structure of struct qrwlock
hidden from qrwlock.h, particularly as it's actually needed for unlock
and ends up being abstracted independently behind the __qrwlock_write_byte()
function.Stop pretending we can hide this stuff, and move the __qrwlock definition
into qrwlock, removing the __qrwlock_write_byte() nastiness and using the
same struct definition everywhere instead.Signed-off-by: Will Deacon
Acked-by: Peter Zijlstra
Cc: Boqun Feng
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Thomas Gleixner
Cc: Waiman Long
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar
10 Oct, 2017
1 commit
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Outside of the locking code itself, {read,spin,write}_can_lock() have no
users in tree. Apparmor (the last remaining user of write_can_lock()) got
moved over to lockdep by the previous patch.This patch removes the use of {read,spin,write}_can_lock() from the
BUILD_LOCK_OPS macro, deferring to the trylock operation for testing the
lock status, and subsequently removes the unused macros altogether. They
aren't guaranteed to work in a concurrent environment and can give
incorrect results in the case of qrwlock.Signed-off-by: Will Deacon
Signed-off-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1507055129-12300-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar
10 Aug, 2016
1 commit
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This patch aims to get rid of endianness in queued_write_unlock(). We
want to set __qrwlock->wmode to NULL, however the address is not
&lock->cnts in big endian machine. That causes queued_write_unlock()
write NULL to the wrong field of __qrwlock.So implement __qrwlock_write_byte() which returns the correct
__qrwlock->wmode address.Suggested-by: Peter Zijlstra (Intel)
Signed-off-by: Pan Xinhui
Signed-off-by: Peter Zijlstra (Intel)
Cc: Andrew Morton
Cc: Linus Torvalds
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Waiman.Long@hpe.com
Cc: arnd@arndb.de
Cc: boqun.feng@gmail.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1468835259-4486-1-git-send-email-xinhui.pan@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar
12 Aug, 2015
2 commits
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The qrwlock implementation is slightly heavy in its use of memory
barriers, mainly through the use of _cmpxchg() and _return() atomics, which
imply full barrier semantics.This patch modifies the qrwlock code to use the more relaxed atomic
routines so that we can reduce the unnecessary barrier overhead on
weakly-ordered architectures.Signed-off-by: Will Deacon
Signed-off-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: Waiman.Long@hp.com
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1438880084-18856-7-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar -
Since the following commit:
536fa402221f ("compiler: Allow 1- and 2-byte smp_load_acquire() and smp_store_release()")
smp_store_release() supports byte accesses, so use that in writer unlock
and remove the conditional macro override.Signed-off-by: Will Deacon
Signed-off-by: Peter Zijlstra (Intel)
Reviewed-by: Waiman Long
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1438880084-18856-6-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar
06 Jul, 2015
2 commits
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The qrwlock is fair in the process context, but becoming unfair when
in the interrupt context to support use cases like the tasklist_lock.The current code isn't that well-documented on what happens when
in the interrupt context. The rspin_until_writer_unlock() will only
spin if the writer has gotten the lock. If the writer is still in the
waiting state, the increment in the reader count will cause the writer
to remain in the waiting state and the new interrupt context reader
will get the lock and return immediately. The current code, however,
does an additional read of the lock value which is not necessary as
the information has already been there in the fast path. This may
sometime cause an additional cacheline transfer when the lock is
highly contended.This patch passes the lock value information gotten in the fast path
to the slow path to eliminate the additional read. It also documents
the action for the interrupt context readers more clearly.Signed-off-by: Waiman Long
Signed-off-by: Peter Zijlstra (Intel)
Reviewed-by: Will Deacon
Cc: Arnd Bergmann
Cc: Douglas Hatch
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Scott J Norton
Cc: Thomas Gleixner
Link: http://lkml.kernel.org/r/1434729002-57724-3-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar -
To sync up with the naming convention used in qspinlock, all the
qrwlock functions were renamed to started with "queued" instead of
"queue".Signed-off-by: Waiman Long
Signed-off-by: Peter Zijlstra (Intel)
Cc: Arnd Bergmann
Cc: Douglas Hatch
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Scott J Norton
Cc: Thomas Gleixner
Cc: Will Deacon
Link: http://lkml.kernel.org/r/1434729002-57724-2-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar
06 Jun, 2014
1 commit
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This rwlock uses the arch_spin_lock_t as a waitqueue, and assuming the
arch_spin_lock_t is a fair lock (ticket,mcs etc..) the resulting
rwlock is a fair lock.It fits in the same 8 bytes as the regular rwlock_t by folding the
reader and writer count into a single integer, using the remaining 4
bytes for the arch_spinlock_t.Architectures that can single-copy adress bytes can optimize
queue_write_unlock() with a 0 write to the LSB (the write count).Performance as measured by Davidlohr Bueso (rwlock_t -> qrwlock_t):
+--------------+-------------+---------------+
| Workload | #users | delta |
+--------------+-------------+---------------+
| alltests | > 1400 | -4.83% |
| custom | 0-100,> 100 | +1.43%,-1.57% |
| high_systime | > 1000 | -2.61 |
| shared | all | +0.32 |
+--------------+-------------+---------------+http://www.stgolabs.net/qrwlock-stuff/aim7-results-vs-rwsem_optsin/
Signed-off-by: Waiman Long
[peterz: near complete rewrite]
Signed-off-by: Peter Zijlstra
Cc: Arnd Bergmann
Cc: Linus Torvalds
Cc: "Paul E.McKenney"
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/n/tip-gac1nnl3wvs2ij87zv2xkdzq@git.kernel.org
Signed-off-by: Ingo Molnar