linux-kernel - Re: [PATCH char-misc 1/1] Drivers: hv: vmbus: Make synic

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Message-ID: <87va7uxl4s.fsf@vitty.brq.redhat.com>
Date:   Tue, 28 Aug 2018 22:59:47 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     "Michael Kelley \(EOSG\)" <Michael.H.Kelley@...rosoft.com>
Cc:     "mhkelley58\@gmail.com" <mhkelley58@...il.com>,
        "gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel\@linuxdriverproject.org" <devel@...uxdriverproject.org>,
        "olaf\@aepfle.de" <olaf@...fle.de>,
        "apw\@canonical.com" <apw@...onical.com>,
        "jasowang\@redhat.com" <jasowang@...hat.com>,
        "marcelo.cerri\@canonical.com" <marcelo.cerri@...onical.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>
Subject: Re: [PATCH char-misc 1/1] Drivers: hv: vmbus: Make synic_initialized flag per-cpu

"Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com> writes:

> From: Vitaly Kuznetsov <vkuznets@...hat.com>  Sent: Wednesday, August 1, 2018 2:26 AM
>
>> > I was trying to decide if there are any arguments in favor of one
>> > approach vs. the other:  a per-cpu flag in memory or checking
>> > the synic_control "enable" bit.   Seems like a wash to me, in which
>> > case I have a slight preference for the per-cpu flag in memory vs.
>> > creating another function to return sctrl.enable.  But I'm completely
>> > open to reasons why checking sctrl.enable is better.
>> 
>> Just a few thoughts: reading MSR is definitely slower but we avoid
>> 'shadowing' the state, the reading is always correct. In case there's a
>> chance the SynIC will get disabled from host side we can only find this
>> out by doing MSR read. This is a purely theoretical possibility, I
>> believe, we can go ahead with this patch.
>
> Vitaly -- just to confirm:  you are OK with the patch as is?  (I'll
> check, but I may need to rebase on the latest code.)

Yes, feel free to use my R-b tag.

-- 
  Vitaly