linux.git/kernel/locking/qspinlock.c, branch v6.12.80

x86/xen: remove deprecated xen_nopvspin boot parameter

2024-07-11T14:33:51+00:00

The xen_nopvspin boot parameter is deprecated since 2019. nopvspin
can be used instead.

Remove the xen_nopvspin boot parameter and replace the xen_pvspin
variable use cases with nopvspin.

This requires to move the nopvspin variable out of the .initdata
section, as it needs to be accessed for cpuhotplug, too.

Signed-off-by: Juergen Gross 
Reviewed-by: Boris Ostrovsky 
Message-ID: <20240710110139.22300-1-jgross@suse.com>
Signed-off-by: Juergen Gross

locking/qspinlock: Use atomic_try_cmpxchg_relaxed() in xchg_tail()

2024-04-11T13:14:54+00:00

Use atomic_try_cmpxchg_relaxed(*ptr, &old, new) instead of
atomic_cmpxchg_relaxed (*ptr, old, new) == old in xchg_tail().

x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after CMPXCHG.

No functional change intended.

Since this code requires NR_CPUS >= 16k, I have tested it
by unconditionally setting _Q_PENDING_BITS to 1 in
.

Signed-off-by: Uros Bizjak 
Signed-off-by: Ingo Molnar 
Reviewed-by: Waiman Long 
Cc: Linus Torvalds 
Link: https://lore.kernel.org/r/20240321195309.484275-1-ubizjak@gmail.com

locking/qspinlock: Micro-optimize pending state waiting for unlock

2023-01-05T10:01:50+00:00

When we're pending, we only care about lock value. The xchg_tail
wouldn't affect the pending state. That means the hardware thread
could stay in a sleep state and leaves the rest execution units'
resources of pipeline to other hardware threads. This situation is
the SMT scenarios in the same core. Not an entering low-power state
situation. Of course, the granularity between cores is "cacheline",
but the granularity between SMT hw threads of the same core could
be "byte" which internal LSU handles. For example, when a hw-thread
yields the resources of the core to other hw-threads, this patch
could help the hw-thread stay in the sleep state and prevent it
from being woken up by other hw-threads xchg_tail.

Signed-off-by: Guo Ren 
Signed-off-by: Guo Ren 
Signed-off-by: Ingo Molnar 
Acked-by: Waiman Long 
Link: https://lore.kernel.org/r/20230105021952.3090070-1-guoren@kernel.org
Cc: Peter Zijlstra

locking: Add __lockfunc to slow path functions

2022-08-19T17:47:51+00:00

So that we can skip the functions in the perf lock contention and other
places like /proc/PID/wchan.

Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Waiman Long 
Link: https://lore.kernel.org/r/20220810220346.1919485-1-namhyung@kernel.org

locking: Apply contention tracepoints in the slow path

2022-04-05T08:24:35+00:00

Adding the lock contention tracepoints in various lock function slow
paths.  Note that each arch can define spinlock differently, I only
added it only to the generic qspinlock for now.

Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Link: https://lkml.kernel.org/r/20220322185709.141236-3-namhyung@kernel.org

x86/kvm: Add "nopvspin" parameter to disable PV spinlocks

2020-07-08T20:21:57+00:00

There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" on XEN platform and
"hv_nopvspin" on HYPER_V).

That feature is missed on KVM, add a new parameter "nopvspin" to disable
PV spinlocks for KVM guest.

The new 'nopvspin' parameter will also replace Xen and Hyper-V specific
parameters in future patches.

Define variable nopvsin as global because it will be used in future
patches as above.

Signed-off-by: Zhenzhong Duan 
Reviewed-by: Vitaly Kuznetsov 
Cc: Jonathan Corbet 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Borislav Petkov 
Cc: "H. Peter Anvin" 
Cc: Paolo Bonzini 
Cc: Radim Krcmar 
Cc: Sean Christopherson 
Cc: Vitaly Kuznetsov 
Cc: Wanpeng Li 
Cc: Jim Mattson 
Cc: Joerg Roedel 
Cc: Peter Zijlstra 
Cc: Will Deacon 
Signed-off-by: Paolo Bonzini

locking/qspinlock: Fix inaccessible URL of MCS lock paper

2020-01-17T09:19:30+00:00

It turns out that the URL of the MCS lock paper listed in the source
code is no longer accessible. I did got question about where the paper
was. This patch updates the URL to BZ 206115 which contains a copy of
the paper from

  https://www.cs.rochester.edu/u/scott/papers/1991_TOCS_synch.pdf

Signed-off-by: Waiman Long 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Will Deacon 
Link: https://lkml.kernel.org/r/20200107174914.4187-1-longman@redhat.com

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157

2019-05-30T18:26:37+00:00

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 details

  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 [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 details

  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 [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 details

extracted 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

locking/qspinlock_stat: Introduce generic lockevent_*() counting APIs

2019-04-10T08:56:03+00:00

The percpu event counts used by qspinlock code can be useful for
other locking code as well. So a new set of lockevent_* counting APIs
is introduced with the lock event names extracted out into the new
lock_events_list.h header file for easier addition in the future.

The existing qstat_inc() calls are replaced by either lockevent_inc() or
lockevent_cond_inc() calls.

The qstat_hop() call is renamed to lockevent_pv_hop(). The "reset_counters"
debugfs file is also renamed to ".reset_counts".

Signed-off-by: Waiman Long 
Acked-by: Peter Zijlstra 
Acked-by: Davidlohr Bueso 
Cc: Andrew Morton 
Cc: Arnd Bergmann 
Cc: Borislav Petkov 
Cc: Davidlohr Bueso 
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Tim Chen 
Cc: Will Deacon 
Link: http://lkml.kernel.org/r/20190404174320.22416-8-longman@redhat.com
Signed-off-by: Ingo Molnar

locking/qspinlock: Remove unnecessary BUG_ON() call

2019-02-28T06:55:38+00:00

With the > 4 nesting levels case handled by the commit:

  d682b596d993 ("locking/qspinlock: Handle > 4 slowpath nesting levels")

the BUG_ON() call in encode_tail() will never actually be triggered.

Remove it.

Signed-off-by: Waiman Long 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Will Deacon 
Cc: Andrew Morton 
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/1551057253-3231-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar