From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f179.google.com (mail-ob0-f179.google.com [209.85.214.179]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id A7A1CB72B4 for ; Mon, 18 Jun 2012 12:52:14 +1000 (EST) Received: by obbeh20 with SMTP id eh20so5531632obb.38 for ; Sun, 17 Jun 2012 19:52:11 -0700 (PDT) Date: Mon, 18 Jun 2012 10:51:59 +0800 From: Yong Zhang To: "Paul E. McKenney" Subject: Re: [RFC PATCH 09/10] POWERPC: smp: remove call to ipi_call_lock()/ipi_call_unlock() Message-ID: <20120618025159.GA24420@zhy> References: <1338275765-3217-1-git-send-email-yong.zhang0@gmail.com> <1338275765-3217-10-git-send-email-yong.zhang0@gmail.com> <20120616163219.GI2420@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <20120616163219.GI2420@linux.vnet.ibm.com> Cc: axboe@kernel.dk, nikunj@linux.vnet.ibm.com, sshtylyov@mvista.com, david.daney@cavium.com, peterz@infradead.org, linux-kernel@vger.kernel.org, ralf@linux-mips.org, akpm@linux-foundation.org, Paul Mackerras , srivatsa.bhat@linux.vnet.ibm.com, tglx@linutronix.de, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org Reply-To: Yong Zhang List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, Jun 16, 2012 at 09:32:19AM -0700, Paul E. McKenney wrote: > On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote: > > From: Yong Zhang > > > > 1) call_function.lock used in smp_call_function_many() is just to protect > > call_function.queue and &data->refs, cpu_online_mask is outside of the > > lock. And it's not necessary to protect cpu_online_mask, > > because data->cpumask is pre-calculate and even if a cpu is brougt up > > when calling arch_send_call_function_ipi_mask(), it's harmless because > > validation test in generic_smp_call_function_interrupt() will take care > > of it. > > > > 2) For cpu down issue, stop_machine() will guarantee that no concurrent > > smp_call_fuction() is processing. > > However, there is an effort to get rid of stop_machine() from the > CPU-down path... So something else will be needed. Yeah. So Thomas changed the commit log like below: [ ipi_call_lock/unlock() lock resp. unlock call_function.lock. This lock protects only the call_function data structure itself, but it's completely unrelated to cpu_online_mask. The mask to which the IPIs are sent is calculated before call_function.lock is taken in smp_call_function_many(), so the locking around set_cpu_online() is pointless and can be removed. [ tglx: Massaged changelog ] ] in tip/smp/hotplug. Thanks, Yong > > Thanx, Paul > > > Signed-off-by: Yong Zhang > > Cc: Benjamin Herrenschmidt > > Cc: Paul Mackerras > > Cc: linuxppc-dev@lists.ozlabs.org > > --- > > arch/powerpc/kernel/smp.c | 2 -- > > 1 files changed, 0 insertions(+), 2 deletions(-) > > > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > > index e4cb343..e1417c4 100644 > > --- a/arch/powerpc/kernel/smp.c > > +++ b/arch/powerpc/kernel/smp.c > > @@ -571,7 +571,6 @@ void __devinit start_secondary(void *unused) > > if (system_state == SYSTEM_RUNNING) > > vdso_data->processorCount++; > > #endif > > - ipi_call_lock(); > > notify_cpu_starting(cpu); > > set_cpu_online(cpu, true); > > /* Update sibling maps */ > > @@ -601,7 +600,6 @@ void __devinit start_secondary(void *unused) > > of_node_put(np); > > } > > of_node_put(l2_cache); > > - ipi_call_unlock(); > > > > local_irq_enable(); > > > > -- > > 1.7.5.4 > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Only stand for myself