From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <konrad.wilk@oracle.com>
Received: from mail.linutronix.de (146.0.238.70:993) by
  crypto-ml.lab.linutronix.de with IMAP4-SSL for <speck@linutronix.de>; 12 Jun
  2018 20:02:14 -0000
Received: from aserp2120.oracle.com ([141.146.126.78])
	by Galois.linutronix.de with esmtps (TLS1.2:RSA_AES_256_CBC_SHA256:256)
	(Exim 4.80)
	(envelope-from <konrad.wilk@oracle.com>)
	id 1fSpUa-0003X1-KR
	for speck@linutronix.de; Tue, 12 Jun 2018 22:02:13 +0200
Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1])
	by aserp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w5CJuOBD038602
	for <speck@linutronix.de>; Tue, 12 Jun 2018 20:02:04 GMT
Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234])
	by aserp2120.oracle.com with ESMTP id 2jgecxjv58-1
	(version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK)
	for <speck@linutronix.de>; Tue, 12 Jun 2018 20:02:04 +0000
Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72])
	by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id w5CK2398005726
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK)
	for <speck@linutronix.de>; Tue, 12 Jun 2018 20:02:04 GMT
Received: from abhmp0010.oracle.com (abhmp0010.oracle.com [141.146.116.16])
	by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w5CK236x013714
	for <speck@linutronix.de>; Tue, 12 Jun 2018 20:02:03 GMT
Date: Tue, 12 Jun 2018 16:02:02 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: [MODERATED] Re: [patch V2 02/12] x86/smp: Provide
 topology_is_primary_thread()
Message-ID: <20180612200202.GQ2462@char.us.oracle.com>
References: <20180606192714.754943543@linutronix.de>
 <20180606192807.093672737@linutronix.de>
 <20180611193245.GB25607@char.us.oracle.com>
 <alpine.DEB.2.21.1806120958580.2157@nanos.tec.linutronix.de>
 <1fce67a1-7eb8-7d08-6d0c-e97309cb5fff@citrix.com>
MIME-Version: 1.0
In-Reply-To: <1fce67a1-7eb8-7d08-6d0c-e97309cb5fff@citrix.com>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
To: speck@linutronix.de
List-ID: <speck.linutronix.de>

On Tue, Jun 12, 2018 at 11:31:50AM +0100, speck for Andrew Cooper wrote:
> On 12/06/18 09:05, speck for Thomas Gleixner wrote:
> > On Mon, 11 Jun 2018, speck for Konrad Rzeszutek Wilk wrote:
> >> On Wed, Jun 06, 2018 at 09:27:16PM +0200, speck for Thomas Gleixner wrote:
> >> Anyhow if we did have four siblings, the mask would end up with 11b
> >> (see below):
> >>
> >> smp_num_siblings	fls	-1	1<<	 -1
> >> 	1 (001b)	1	0	1	0
> >> 	2 (010b)	2	1	2	01b
> >> 	4 (100b)	3	2	4	11b
> > That's what I intended :)
> >
> >>> +	return !(apicid & mask);
> >> So with an normal 2-sibling, say APICID 0x76 and 0x77 with mask 1b:
> >>
> >> 	0x76	01110110b & 01 -> !0 -> return 1
> >> 	0x77	01110111b & 01 -> !1 -> return 0
> >>
> >> that looks good.
> >>
> >> If this is a 4 thread. APICID 0x4, 0x5, and 0x6
> >>
> >> 	0x4	0100 & 11b -> 00 -> !0 -> return 1
> >> 	0x5	0101 & 11b -> 01 -> !1 -> return 0 
> >> 	0x6	0110 & 11b -> 10 -> !1111..1101 -> return 0xffff..which cast to bool is 'true' [BAD]
> >>
> >> That is the 3rd sibling would be incorrectly identified as primary thread.
> >>
> >> I think? I would welcome somebody checking my logic over, but then
> >> perhaps this is non-issue-b/c-we-don-do more than 2 so go away.
> > You are somehow confusing '!' and '~'

<blushes>

Um, moving right along..

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

> 
> The original logic looks correct to me, and matches my equivalent in Xen.
> 
> ~Andrew