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

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Message-ID: <CY4PR21MB077375C31D9211486C328328DC0A0@CY4PR21MB0773.namprd21.prod.outlook.com>
Date:   Tue, 28 Aug 2018 20:20:19 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     vkuznets <vkuznets@...hat.com>
CC:     "mhkelley58@...il.com" <mhkelley58@...il.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "marcelo.cerri@...onical.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

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.)

Michael