From: Waiman Long <llong@redhat.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Waiman Long <llong@redhat.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Tejun Heo <tj@kernel.org>, Barret Rhoden <brho@google.com>,
Josh Don <joshdon@google.com>, Dohyun Kim <dohyunkim@google.com>,
kernel-team@meta.com
Subject: Re: [PATCH bpf-next v1 12/22] rqspinlock: Add basic support for CONFIG_PARAVIRT
Date: Wed, 8 Jan 2025 11:27:12 -0500 [thread overview]
Message-ID: <2eaf52fb-b7d4-4024-a671-02d5375fca22@redhat.com> (raw)
In-Reply-To: <20250107140004.2732830-13-memxor@gmail.com>
On 1/7/25 8:59 AM, Kumar Kartikeya Dwivedi wrote:
> We ripped out PV and virtualization related bits from rqspinlock in an
> earlier commit, however, a fair lock performs poorly within a virtual
> machine when the lock holder is preempted. As such, retain the
> virt_spin_lock fallback to test and set lock, but with timeout and
> deadlock detection.
>
> We don't integrate support for CONFIG_PARAVIRT_SPINLOCKS yet, as that
> requires more involved algorithmic changes and introduces more
> complexity. It can be done when the need arises in the future.
virt_spin_lock() doesn't scale well. It is for hypervisors that don't
support PV qspinlock yet. Now rqspinlock() will be in this category.
I wonder if we should provide an option to disable rqspinlock and fall
back to the regular qspinlock with strict BPF locking semantics.
Another question that I have is about PREEMPT_RT kernel which cannot
tolerate any locking stall. That will probably require disabling
rqspinlock if CONFIG_PREEMPT_RT is enabled.
Cheers,
Longman
next prev parent reply other threads:[~2025-01-08 16:27 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-07 13:59 [PATCH bpf-next v1 00/22] Resilient Queued Spin Lock Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 01/22] locking: Move MCS struct definition to public header Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 02/22] locking: Move common qspinlock helpers to a private header Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 03/22] locking: Allow obtaining result of arch_mcs_spin_lock_contended Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 04/22] locking: Copy out qspinlock.c to rqspinlock.c Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 05/22] rqspinlock: Add rqspinlock.h header Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 06/22] rqspinlock: Drop PV and virtualization support Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 07/22] rqspinlock: Add support for timeouts Kumar Kartikeya Dwivedi
2025-01-07 14:50 ` Peter Zijlstra
2025-01-07 17:14 ` Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 08/22] rqspinlock: Protect pending bit owners from stalls Kumar Kartikeya Dwivedi
2025-01-07 14:51 ` Peter Zijlstra
2025-01-07 17:14 ` Kumar Kartikeya Dwivedi
2025-01-07 19:17 ` Peter Zijlstra
2025-01-07 19:22 ` Peter Zijlstra
2025-01-07 19:54 ` Kumar Kartikeya Dwivedi
2025-01-08 2:19 ` Waiman Long
2025-01-08 20:13 ` Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 09/22] rqspinlock: Protect waiters in queue " Kumar Kartikeya Dwivedi
2025-01-08 3:38 ` Waiman Long
2025-01-08 20:42 ` Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 10/22] rqspinlock: Protect waiters in trylock fallback " Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 11/22] rqspinlock: Add deadlock detection and recovery Kumar Kartikeya Dwivedi
2025-01-08 16:06 ` Waiman Long
2025-01-08 20:19 ` Kumar Kartikeya Dwivedi
2025-01-09 0:32 ` Waiman Long
2025-01-07 13:59 ` [PATCH bpf-next v1 12/22] rqspinlock: Add basic support for CONFIG_PARAVIRT Kumar Kartikeya Dwivedi
2025-01-08 16:27 ` Waiman Long [this message]
2025-01-08 20:32 ` Kumar Kartikeya Dwivedi
2025-01-09 0:48 ` Waiman Long
2025-01-09 2:42 ` Alexei Starovoitov
2025-01-09 2:58 ` Waiman Long
2025-01-09 3:37 ` Alexei Starovoitov
2025-01-09 3:46 ` Waiman Long
2025-01-09 3:53 ` Alexei Starovoitov
2025-01-09 3:58 ` Waiman Long
2025-01-07 13:59 ` [PATCH bpf-next v1 13/22] rqspinlock: Add helper to print a splat on timeout or deadlock Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 14/22] rqspinlock: Add macros for rqspinlock usage Kumar Kartikeya Dwivedi
2025-01-08 16:55 ` Waiman Long
2025-01-08 20:41 ` Kumar Kartikeya Dwivedi
2025-01-09 1:11 ` Waiman Long
2025-01-09 3:30 ` Alexei Starovoitov
2025-01-09 4:09 ` Waiman Long
2025-01-07 13:59 ` [PATCH bpf-next v1 15/22] rqspinlock: Add locktorture support Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 16/22] rqspinlock: Add entry to Makefile, MAINTAINERS Kumar Kartikeya Dwivedi
2025-01-07 13:59 ` [PATCH bpf-next v1 17/22] bpf: Convert hashtab.c to rqspinlock Kumar Kartikeya Dwivedi
2025-01-07 14:00 ` [PATCH bpf-next v1 18/22] bpf: Convert percpu_freelist.c " Kumar Kartikeya Dwivedi
2025-01-07 14:00 ` [PATCH bpf-next v1 19/22] bpf: Convert lpm_trie.c " Kumar Kartikeya Dwivedi
2025-01-07 14:00 ` [PATCH bpf-next v1 20/22] bpf: Introduce rqspinlock kfuncs Kumar Kartikeya Dwivedi
2025-01-08 10:23 ` kernel test robot
2025-01-08 10:23 ` kernel test robot
2025-01-08 10:44 ` kernel test robot
2025-01-07 14:00 ` [PATCH bpf-next v1 21/22] bpf: Implement verifier support for rqspinlock Kumar Kartikeya Dwivedi
2025-01-07 14:00 ` [PATCH bpf-next v1 22/22] selftests/bpf: Add tests " Kumar Kartikeya Dwivedi
2025-01-07 23:54 ` [PATCH bpf-next v1 00/22] Resilient Queued Spin Lock Linus Torvalds
2025-01-08 9:18 ` Peter Zijlstra
2025-01-08 20:12 ` Kumar Kartikeya Dwivedi
2025-01-08 20:30 ` Linus Torvalds
2025-01-08 21:06 ` Kumar Kartikeya Dwivedi
2025-01-08 21:30 ` Paul E. McKenney
2025-01-09 13:59 ` Waiman Long
2025-01-09 21:13 ` Kumar Kartikeya Dwivedi
2025-01-09 21:18 ` Waiman Long
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