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

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Message-ID: <CY4PR21MB0773EFCF6EA21CF8F9CE01E0DC2D0@CY4PR21MB0773.namprd21.prod.outlook.com>
Date:   Wed, 1 Aug 2018 05:47:08 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        "mhkelley58@...il.com" <mhkelley58@...il.com>
CC:     "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: Tuesday, July 31, 2018 4:20 AM
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

Thanks for the review

> 
> Alternatively, we can get rid of synic_initialized flag altogether:
> hv_synic_init() never fails in the first place but we can always
> implement something like:
> 
> int hv_synic_is_initialized(void) {
> 	union hv_synic_scontrol sctrl;
> 
> 	hv_get_synic_state(sctrl.as_uint64);
> 
> 	return sctrl.enable;
> }
> 
> as it doesn't seem that we need to check synic state on _other_ CPUs.
> 
> --
>   Vitaly

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.

Michael