From: Sean Christopherson <seanjc@google.com>
To: Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Will Deacon <will@kernel.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
Valentin Schneider <valentin.schneider@arm.com>,
Marco Elver <elver@google.com>,
Frederic Weisbecker <frederic@kernel.org>,
David Matlack <dmatlack@google.com>,
Friedrich Weber <f.weber@proxmox.com>,
Ankur Arora <ankur.a.arora@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2 0/2] sched/core: Fix spinlocks vs. PREEMPT_DYNAMIC=y
Date: Wed, 24 Apr 2024 13:08:25 -0700 [thread overview]
Message-ID: <ZilmuTJzyk7U-Kul@google.com> (raw)
In-Reply-To: <20240312193911.1796717-1-seanjc@google.com>
On Tue, Mar 12, 2024, Sean Christopherson wrote:
> Fix a bug in dynamic preemption where the kernel will yield contended
> spinlocks (and rwlocks) even if the selected preemption model is "none" or
> "voluntary". I say "bug" because this divergence from PREEMPT_DYNAMIC=n
> behavior effectively broke existing KVM configurations, e.g. vCPUs would
> get stuck and become unresponsive for multiple seconds if there was heavy
> KSM or NUMA balancing activity in the host.
>
> This isn't super urgent, as 6.8 has a fix in KVM for the over-aggressive
> yielding (commit d02c357e5bfa ("KVM: x86/mmu: Retry fault before acquiring
> mmu_lock if mapping is changing"), but I wouldn't be surprised if the
> behavior is causing other performance issues/regressions that are less
> severe and/or less visible.
Anyone have any thoughts on how to move this forward? I have a hard time
believing no one has opinions on this code :-)
> v2:
> - Rebase onto Linus' tree to deal with the code movement to spinlock.h.
> - Opportunistically document the behavior.
> - Add the PREEMPT_AUTO folks to Cc to get their eyeballs/input.
>
> v1: https://lore.kernel.org/all/20240110214723.695930-1-seanjc@google.com
>
> Sean Christopherson (2):
> sched/core: Move preempt_model_*() helpers from sched.h to preempt.h
> sched/core: Drop spinlocks on contention iff kernel is preemptible
>
> .../admin-guide/kernel-parameters.txt | 4 +-
> include/linux/preempt.h | 41 +++++++++++++++++++
> include/linux/sched.h | 41 -------------------
> include/linux/spinlock.h | 14 +++----
> 4 files changed, 50 insertions(+), 50 deletions(-)
>
>
> base-commit: b29f377119f68b942369a9366bdcb1fec82b2cda
> --
> 2.44.0.278.ge034bb2e1d-goog
>
prev parent reply other threads:[~2024-04-24 20:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-12 19:39 [PATCH v2 0/2] sched/core: Fix spinlocks vs. PREEMPT_DYNAMIC=y Sean Christopherson
2024-03-12 19:39 ` [PATCH v2 1/2] sched/core: Move preempt_model_*() helpers from sched.h to preempt.h Sean Christopherson
2024-04-25 6:19 ` Ankur Arora
2024-03-12 19:39 ` [PATCH v2 2/2] sched/core: Drop spinlocks on contention iff kernel is preemptible Sean Christopherson
2024-04-25 6:18 ` Ankur Arora
2024-04-25 7:41 ` Chen Yu
2024-04-25 16:47 ` Sean Christopherson
2024-04-26 3:41 ` Chen Yu
2024-04-24 20:08 ` Sean Christopherson [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ZilmuTJzyk7U-Kul@google.com \
--to=seanjc@google.com \
--cc=ankur.a.arora@oracle.com \
--cc=corbet@lwn.net \
--cc=dmatlack@google.com \
--cc=elver@google.com \
--cc=f.weber@proxmox.com \
--cc=frederic@kernel.org \
--cc=juri.lelli@redhat.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=valentin.schneider@arm.com \
--cc=vincent.guittot@linaro.org \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).