From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Suleiman Souhlal <suleiman@google.com>,
rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rcu/tree: consider time a VM was suspended
Date: Fri, 21 May 2021 15:42:31 +0900 [thread overview]
Message-ID: <YKdWV2lznaxUKBM5@google.com> (raw)
In-Reply-To: <20210521001443.GR4441@paulmck-ThinkPad-P17-Gen-1>
On (21/05/20 17:14), Paul E. McKenney wrote:
> > On a side note.
> >
> > I wish we didn't have to put kvm_check_and_clear_guest_paused() all
> > over the place.
> >
> > We do load jiffies at the start of check_cpu_stall(). So, in theory,
> > we can just use that captured jiffies (which can become obsolete but
> > so will grace period timestamps) value and never read current system
> > jiffies because they can jump way forward. IOW
> >
> > jn = j + 3 * rcu_jiffies_till_stall_check() + 3;
> >
> > instead of
> >
> > jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
> >
> > Then we probably can remove kvm_check_and_clear_guest_paused().
> >
> > But that "don't load current jiffies" is rather fragile.
> >
> > kvm_check_and_clear_guest_paused() is not pretty, but at least it's
> > explicit.
>
> If this works for you, I am very much in favor!
Oh, no. Sorry for the noise. This is racy and won't work.
next prev parent reply other threads:[~2021-05-21 6:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-16 10:27 [PATCH] rcu/tree: consider time a VM was suspended Sergey Senozhatsky
2021-05-17 16:23 ` Paul E. McKenney
2021-05-18 1:41 ` Sergey Senozhatsky
2021-05-18 23:15 ` Paul E. McKenney
2021-05-20 5:50 ` Sergey Senozhatsky
2021-05-20 14:57 ` Paul E. McKenney
2021-05-20 22:34 ` Sergey Senozhatsky
2021-05-21 0:15 ` Paul E. McKenney
2021-05-20 6:18 ` Sergey Senozhatsky
2021-05-20 14:53 ` Paul E. McKenney
2021-05-20 22:24 ` Sergey Senozhatsky
2021-05-21 0:14 ` Paul E. McKenney
2021-05-21 6:42 ` Sergey Senozhatsky [this message]
2021-05-21 14:02 ` Paul E. McKenney
2021-05-21 6:36 ` Sergey Senozhatsky
2021-05-21 14:01 ` Paul E. McKenney
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