From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Dexuan Cui <decui@microsoft.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
"devel\@linuxdriverproject.org" <devel@linuxdriverproject.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
KY Srinivasan <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>
Subject: Re: [PATCH 0/7] hv: CPU onlining/offlining fixes and improvements
Date: Mon, 28 Nov 2016 10:12:05 +0100 [thread overview]
Message-ID: <87twasezoa.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <MWHPR03MB26692E612C3599E12BF7C8DBBF8A0@MWHPR03MB2669.namprd03.prod.outlook.com> (Dexuan Cui's message of "Mon, 28 Nov 2016 06:56:23 +0000")
Dexuan Cui <decui@microsoft.com> writes:
>> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
>> Sent: Sunday, November 27, 2016 01:06
>> To: Vitaly Kuznetsov <vkuznets@redhat.com>
>> Cc: devel@linuxdriverproject.org; linux-kernel@vger.kernel.org; KY Srinivasan
>> <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Dexuan Cui
>> <decui@microsoft.com>
>> Subject: Re: [PATCH 0/7] hv: CPU onlining/offlining fixes and improvements
>>
>> On Fri, 25 Nov 2016 13:48:36 +0100
>> Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>>
>> > Some time ago we forbade CPU offlining for Hyper-V and this was sufficient
>> > if you boot with all CPUs onlined. Turns out, people may want to limit the
>> > number online CPUs by passing 'maxcpus=' kernel parameter and we hit a
>> > crash in Hyper-V code in this case. After some thinking, I think we may not
>> > only fix the crash but also make the offlining prevention fine-grained: we
>> > need to prevent from offlining CPUs which have VMBus channels attached
>> > only. All offlined CPUs may always be onlined.
>> >
>>
>> As a temporary solution this is ok, but long term we need to support
>> dynamic CPU online/offline.
>
> If a CPU is bound to some channels, it seems impossible to make it offline,
> unless Hyper-V supplies a mechanism to dynamically rebind the channels (i.e.
> without closing & opening the channels) to another CPU, e.g. CPU0.
> Currently it looks there is no such mechanism.
>
Exactly. Offlining a CPU with an attached active VMBus channel means
killing the device and unless we're offereed an API to rebind it to some
other CPU there is no point in allowing that. We may, however, allow
offlining CPUs with sub-channels attached by closing these sub-channels,
not sure if we want to.
--
Vitaly
next prev parent reply other threads:[~2016-11-28 9:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-25 12:48 [PATCH 0/7] hv: CPU onlining/offlining fixes and improvements Vitaly Kuznetsov
2016-11-25 12:48 ` [PATCH 1/7] hv: acquire vmbus_connection.channel_mutex in vmbus_free_channels() Vitaly Kuznetsov
2016-11-28 6:20 ` Dexuan Cui
2016-11-25 12:48 ` [PATCH 2/7] hv: allocate synic pages for all present CPUs Vitaly Kuznetsov
2016-11-25 12:48 ` [PATCH 3/7] hv: init percpu_list in hv_synic_alloc() Vitaly Kuznetsov
2016-11-25 12:48 ` [PATCH 4/7] hv: change clockevents unbind tactics Vitaly Kuznetsov
2016-11-25 12:48 ` [PATCH 5/7] hv: check all present cpus in vmbus_wait_for_unload() Vitaly Kuznetsov
2016-11-25 12:48 ` [PATCH 6/7] hv: switch to cpuhp state machine for synic init/cleanup Vitaly Kuznetsov
2016-11-25 12:48 ` [PATCH 7/7] hv: make CPU offlining prevention fine-grained Vitaly Kuznetsov
2016-11-26 17:05 ` [PATCH 0/7] hv: CPU onlining/offlining fixes and improvements Stephen Hemminger
2016-11-28 6:56 ` Dexuan Cui
2016-11-28 9:12 ` Vitaly Kuznetsov [this message]
2017-01-02 19:49 ` Vitaly Kuznetsov
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=87twasezoa.fsf@vitty.brq.redhat.com \
--to=vkuznets@redhat.com \
--cc=decui@microsoft.com \
--cc=devel@linuxdriverproject.org \
--cc=haiyangz@microsoft.com \
--cc=kys@microsoft.com \
--cc=linux-kernel@vger.kernel.org \
--cc=stephen@networkplumber.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