From: Jan Beulich <jbeulich@suse.com>
To: Juergen Gross <jgross@suse.com>
Cc: "Kevin Tian" <kevin.tian@intel.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Julien Grall" <julien@xen.org>, "Wei Liu" <wl@xen.org>,
"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Ross Lagerwall" <ross.lagerwall@citrix.com>,
"Jun Nakajima" <jun.nakajima@intel.com>,
xen-devel@lists.xenproject.org,
"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH] xen: do live patching only from main idle loop
Date: Wed, 12 Feb 2020 10:46:45 +0100 [thread overview]
Message-ID: <bdccae10-21bc-bb19-b650-f3b97fb58a5a@suse.com> (raw)
In-Reply-To: <20200211093122.5644-1-jgross@suse.com>
On 11.02.2020 10:31, Juergen Gross wrote:
> One of the main design goals of core scheduling is to avoid actions
> which are not directly related to the domain currently running on a
> given cpu or core. Live patching is one of those actions which are
> allowed taking place on a cpu only when the idle scheduling unit is
> active on that cpu.
>
> Unfortunately live patching tries to force the cpus into the idle loop
> just by raising the schedule softirq, which will no longer be
> guaranteed to work with core scheduling active. Additionally there are
> still some places in the hypervisor calling check_for_livepatch_work()
> without being in the idle loop.
>
> It is easy to force a cpu into the main idle loop by scheduling a
> tasklet on it. So switch live patching to use tasklets for switching to
> idle and raising scheduling events. Additionally the calls of
> check_for_livepatch_work() outside the main idle loop can be dropped.
>
> As tasklets are only running on idle vcpus and stop_machine_run()
> is activating tasklets on all cpus but the one it has been called on
> to rendezvous, it is mandatory for stop_machine_run() to be called on
> an idle vcpu, too, as otherwise there is no way for scheduling to
> activate the idle vcpu for the tasklet on the sibling of the cpu
> stop_machine_run() has been called on.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
Applicable x86 bits
Acked-by: Jan Beulich <jbeulich@suse.com>
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next prev parent reply other threads:[~2020-02-12 9:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 9:31 [Xen-devel] [PATCH] xen: do live patching only from main idle loop Juergen Gross
2020-02-12 9:46 ` Jan Beulich [this message]
2020-02-18 5:41 ` Tian, Kevin
2020-02-24 22:25 ` Julien Grall
2020-02-26 14:17 ` Jürgen Groß
2020-02-27 21:51 ` Julien Grall
2020-03-02 14:28 ` Jan Beulich
2020-03-02 14:41 ` Ross Lagerwall
2020-03-02 18:34 ` Konrad Rzeszutek Wilk
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