From: Mathieu Desnoyers <mathieu.desnoyers@efficios•com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: Thomas Gleixner <tglx@linutronix•de>,
Ingo Molnar <mingo@redhat•com>,
Juri Lelli <juri.lelli@redhat•com>,
Vincent Guittot <vincent.guittot@linaro•org>,
Dietmar Eggemann <dietmar.eggemann@arm•com>,
rostedt <rostedt@goodmis•org>, Ben Segall <bsegall@google•com>,
Mel Gorman <mgorman@suse•de>, bristot <bristot@redhat•com>,
Borislav Petkov <bp@alien8•de>, x86 <x86@kernel•org>,
"H. Peter Anvin" <hpa@zytor•com>, Jens Axboe <axboe@kernel•dk>,
Alasdair Kergon <agk@redhat•com>,
Mike Snitzer <snitzer@redhat•com>,
dm-devel@redhat•com, "David S. Miller" <davem@davemloft•net>,
Jakub Kicinski <kuba@kernel•org>, Felipe Balbi <balbi@kernel•org>,
Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
Alexander Viro <viro@zeniv•linux.org.uk>,
Tejun Heo <tj@kernel•org>, Zefan Li <lizefan.x@bytedance•com>,
Johannes Weiner <hannes@cmpxchg•org>,
Jason Wessel <jason.wessel@windriver•com>,
Daniel Thompson <daniel.thompson@linaro•org>,
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Mark Rutland <mark.rutland@arm•com>,
Alexander Shishkin <alexander.shishkin@linux•intel.com>,
Jiri Olsa <jolsa@redhat•com>, Namhyung Kim <namhyung@kernel•org>,
"Rafael J. Wysocki" <rjw@rjwysocki•net>,
Pavel Machek <pavel@ucw•cz>, Will Deacon <will@kernel•org>,
Waiman Long <longman@redhat•com>,
Boqun Feng <boqun.feng@gmail•com>,
Oleg Nesterov <oleg@redhat•com>,
Davidlohr Bueso <dave@stgolabs•net>, paulmck <paulmck@kernel•org>,
Josh Triplett <josh@joshtriplett•org>,
Lai Jiangshan <jiangshanlai@gmail•com>,
"Joel Fernandes, Google" <joel@joelfernandes•org>,
John Stultz <john.stultz@linaro•org>,
Stephen Boyd <sboyd@kernel•org>,
Andrew Morton <akpm@linux-foundation•org>,
Paolo Bonzini <pbonzini@redhat•com>,
linux-kernel <linux-kernel@vger•kernel.org>,
linux-block@vger•kernel.org, netdev <netdev@vger•kernel.org>,
linux-usb@vger•kernel.org,
linux-fsdevel <linux-fsdevel@vger•kernel.org>,
cgroups <cgroups@vger•kernel.org>,
kgdb-bugreport@lists•sourceforge.net,
linux-perf-users@vger•kernel.org, linux-pm@vger•kernel.org,
rcu <rcu@vger•kernel.org>, linux-mm <linux-mm@kvack•org>,
KVM list <kvm@vger•kernel.org>
Subject: Re: [PATCH 3/6] sched,perf,kvm: Fix preemption condition
Date: Wed, 2 Jun 2021 09:59:07 -0400 (EDT) [thread overview]
Message-ID: <1873020549.5854.1622642347895.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20210602133040.398289363@infradead.org>
----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz@infradead•org wrote:
> When ran from the sched-out path (preempt_notifier or perf_event),
> p->state is irrelevant to determine preemption. You can get preempted
> with !task_is_running() just fine.
>
> The right indicator for preemption is if the task is still on the
> runqueue in the sched-out path.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead•org>
> ---
> kernel/events/core.c | 7 +++----
> virt/kvm/kvm_main.c | 2 +-
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8568,13 +8568,12 @@ static void perf_event_switch(struct tas
> },
> };
>
> - if (!sched_in && task->state == TASK_RUNNING)
> + if (!sched_in && current->on_rq) {
This changes from checking task->state to current->on_rq, but this change
from "task" to "current" is not described in the commit message, which is odd.
Are we really sure that task == current here ?
Thanks,
Mathieu
> switch_event.event_id.header.misc |=
> PERF_RECORD_MISC_SWITCH_OUT_PREEMPT;
> + }
>
> - perf_iterate_sb(perf_event_switch_output,
> - &switch_event,
> - NULL);
> + perf_iterate_sb(perf_event_switch_output, &switch_event, NULL);
> }
>
> /*
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4869,7 +4869,7 @@ static void kvm_sched_out(struct preempt
> {
> struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
>
> - if (current->state == TASK_RUNNING) {
> + if (current->on_rq) {
> WRITE_ONCE(vcpu->preempted, true);
> WRITE_ONCE(vcpu->ready, true);
> }
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2021-06-02 13:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-02 13:12 [PATCH 0/6] sched: Cleanup task_struct::state Peter Zijlstra
2021-06-02 13:12 ` [PATCH 1/6] sched: Unbreak wakeups Peter Zijlstra
2021-06-02 13:58 ` Greg Kroah-Hartman
2021-06-02 14:47 ` Will Deacon
2021-06-02 19:43 ` Davidlohr Bueso
2021-06-02 13:12 ` [PATCH 2/6] sched: Introduce task_is_running() Peter Zijlstra
2021-06-02 14:59 ` Will Deacon
2021-06-02 16:46 ` Peter Zijlstra
2021-06-02 23:15 ` Davidlohr Bueso
2021-06-02 13:12 ` [PATCH 3/6] sched,perf,kvm: Fix preemption condition Peter Zijlstra
2021-06-02 13:59 ` Mathieu Desnoyers [this message]
2021-06-02 14:10 ` Peter Zijlstra
2021-06-02 14:30 ` Mark Rutland
2021-06-02 14:15 ` Mathieu Desnoyers
2021-06-02 14:23 ` Peter Zijlstra
2021-06-02 13:12 ` [PATCH 4/6] sched: Add get_current_state() Peter Zijlstra
2021-06-02 14:01 ` Mathieu Desnoyers
2021-06-02 14:12 ` Peter Zijlstra
2021-06-02 15:02 ` Will Deacon
2021-06-02 13:12 ` [PATCH 5/6] sched,timer: Use __set_current_state() Peter Zijlstra
2021-06-02 15:06 ` Will Deacon
2021-06-02 19:54 ` Davidlohr Bueso
2021-06-03 6:39 ` Peter Zijlstra
2021-06-18 20:42 ` Thomas Gleixner
2021-06-02 13:12 ` [PATCH 6/6] sched: Change task_struct::state Peter Zijlstra
2021-06-02 14:06 ` Mathieu Desnoyers
2021-06-02 14:20 ` Peter Zijlstra
2021-06-02 15:10 ` Will Deacon
2021-06-07 10:45 ` Daniel Thompson
2021-06-07 11:10 ` Peter Zijlstra
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