Re: (subset) [PATCH v3 00/17] powerpc: alternate queued spinlock implementation

On Sat, 26 Nov 2022 19:59:15 +1000, Nicholas Piggin wrote:

This replaces the generic queued spinlock code (like s390 does) with
our own implementation. There is an extra shim patch 1a to get the
series to apply.

Generic PV qspinlock code is causing latency / starvation regressions on
large systems that are resulting in hard lockups reported (mostly in
pathoogical cases).  The generic qspinlock code has a number of issues
important for powerpc hardware and hypervisors that aren't easily solved
without changing code that would impact other architectures. Follow
s390's lead and implement our own for now.

[...]

Applied to powerpc/next.

[00/17] powerpc/qspinlock: powerpc qspinlock implementation
        https://git.kernel.org/powerpc/c/9f61521c7a284e799050cd2adacc9a611bd2b491
[01/17] powerpc/qspinlock: add mcs queueing for contended waiters
        https://git.kernel.org/powerpc/c/84990b169557428c318df87b7836cd15f65b62dc
[02/17] powerpc/qspinlock: use a half-word store to unlock to avoid larx/stcx.
        https://git.kernel.org/powerpc/c/4c93c2e4b9e8988511c06b9c042f23d4b8f593ad
[03/17] powerpc/qspinlock: convert atomic operations to assembly
        https://git.kernel.org/powerpc/c/b3a73b7db2b6cb3b2e5bfda5518a0e92230ef673
[04/17] powerpc/qspinlock: allow new waiters to steal the lock before queueing
        https://git.kernel.org/powerpc/c/6aa42f883c438ea132a28801bef3f86f3883d14c
[05/17] powerpc/qspinlock: theft prevention to control latency
        https://git.kernel.org/powerpc/c/0944534ef4d5cf39c8133575524be0be3337dd62
[06/17] powerpc/qspinlock: store owner CPU in lock word
        https://git.kernel.org/powerpc/c/e1a31e7fd7130628cfd229253da2b4630e7a809c
[07/17] powerpc/qspinlock: paravirt yield to lock owner
        https://git.kernel.org/powerpc/c/085f03311bcede99550e08a1f7cad41bf758b460
[08/17] powerpc/qspinlock: implement option to yield to previous node
        https://git.kernel.org/powerpc/c/bd48287b2cf4cd6e95576db3a94fd2a7cdf9832d
[09/17] powerpc/qspinlock: allow stealing when head of queue yields
        https://git.kernel.org/powerpc/c/b4c3cdc1a698a2f6168768d0bed4bf062723722e
[10/17] powerpc/qspinlock: allow propagation of yield CPU down the queue
        https://git.kernel.org/powerpc/c/28db61e207ea3890d286cff3141c1ce67346074d
[11/17] powerpc/qspinlock: add ability to prod new queue head CPU
        https://git.kernel.org/powerpc/c/be742c573fdafcfa1752642ca1c7aaf08c258128
[12/17] powerpc/qspinlock: allow lock stealing in trylock and lock fastpath
        https://git.kernel.org/powerpc/c/f61ab43cc1a6146d6eef7e0713a452c3677ad13e
[13/17] powerpc/qspinlock: use spin_begin/end API
        https://git.kernel.org/powerpc/c/71c235027ce7940434acd3f553602ad8b5d36469
[14/17] powerpc/qspinlock: reduce remote node steal spins
        https://git.kernel.org/powerpc/c/cc79701114154efe79663ba47d9e51aad2ed3c78
[15/17] powerpc/qspinlock: allow indefinite spinning on a preempted owner
        https://git.kernel.org/powerpc/c/39dfc73596b48bb50cf7e4f3f54e38427dda5b4e
[16/17] powerpc/qspinlock: provide accounting and options for sleepy locks
        https://git.kernel.org/powerpc/c/12b459a5ebf3308e718bc1dd48acb7c4cf7f1a75
[17/17] powerpc/qspinlock: add compile-time tuning adjustments
        https://git.kernel.org/powerpc/c/0b2199841a7952d01a717b465df028b40b2cf3e9

cheers