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[61.68.186.125]) by smtp.gmail.com with ESMTPSA id i128sm8838706pfe.74.2020.07.02.03.36.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Jul 2020 03:36:33 -0700 (PDT) Date: Thu, 02 Jul 2020 20:36:27 +1000 From: Nicholas Piggin Subject: Re: [PATCH 2/8] powerpc/pseries: use smp_rmb() in H_CONFER spin yield To: Peter Zijlstra References: <20200702074839.1057733-1-npiggin@gmail.com> <20200702074839.1057733-3-npiggin@gmail.com> <20200702082840.GC4781@hirez.programming.kicks-ass.net> In-Reply-To: <20200702082840.GC4781@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Message-Id: <1593685552.uh4kepm08t.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Will Deacon , Boqun Feng , linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , Waiman Long , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Excerpts from Peter Zijlstra's message of July 2, 2020 6:28 pm: > On Thu, Jul 02, 2020 at 05:48:33PM +1000, Nicholas Piggin wrote: >> There is no need for rmb(), this allows faster lwsync here. >=20 > Since you determined this; I'm thinking you actually understand the > ordering here. How about recording this understanding in a comment? >=20 > Also, should the lock->slock load not use READ_ONCE() ? Yeah, good point. Maybe I'll drop it from this series, doesn't really=20 belong I just saw the cleanup and didn't want to forget it. We we just ordering the two loads in this function, and !SMP isn't a=20 concern (i.e., no issues of !SMP guest on SMP HV), but yeah fixing the lack of comment is warranted, thanks. Thanks, Nick