From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Date: Fri, 05 Sep 2014 20:09:26 +0000 Subject: Re: bit fields && data tearing Message-Id: <20140905200926.GW5001@linux.vnet.ibm.com> List-Id: References: <063D6719AE5E284EB5DD2968C1650D6D17487172@AcuExch.aculab.com> <1409824374.4246.62.camel@pasglop> <5408E458.3@zytor.com> <54090AF4.7060406@hurleysoftware.com> <54091B30.2090509@zytor.com> <20140905081648.GB5281@omega> <20140905180950.GU5001@linux.vnet.ibm.com> <540A05F7.1070202@hurleysoftware.com> <20140905190506.GV5001@linux.vnet.ibm.com> <540A0DF3.8030802@hurleysoftware.com> In-Reply-To: <540A0DF3.8030802@hurleysoftware.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Hurley Cc: Michael Cree , "H. Peter Anvin" , Benjamin Herrenschmidt , David Laight , Jakub Jelinek , "linux-arch@vger.kernel.org" , Tony Luck , "linux-ia64@vger.kernel.org" , Oleg Nesterov , "linux-kernel@vger.kernel.org" , Paul Mackerras , "linuxppc-dev@lists.ozlabs.org" , Miroslav Franc , Richard Henderson , linux-alpha@vger.kernel.org On Fri, Sep 05, 2014 at 03:24:35PM -0400, Peter Hurley wrote: > On 09/05/2014 03:05 PM, Paul E. McKenney wrote: > > On Fri, Sep 05, 2014 at 02:50:31PM -0400, Peter Hurley wrote: > >> On 09/05/2014 02:09 PM, Paul E. McKenney wrote: > > [cut] > > >>> ------------------------------------------------------------------------ > >>> > >>> documentation: Record limitations of bitfields and small variables > >>> > >>> This commit documents the fact that it is not safe to use bitfields as > >>> shared variables in synchronization algorithms. It also documents that > >>> CPUs must provide one-byte and two-byte load and store instructions > >> ^ > >> atomic > > > > Here you meant non-atomic? My guess is that you are referring to the > > fact that you could emulate a one-byte store on pre-EV56 Alpha CPUs > > using the ll and sc atomic-read-modify-write instructions, correct? > > Yes, that's what I meant. I must be tired and am misreading the commit > message, or misinterpreting it's meaning. Very good, got it! Thanx, Paul