From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id D3764B7D03 for ; Fri, 29 Jan 2010 13:02:54 +1100 (EST) Subject: Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt_power for Power7 From: Benjamin Herrenschmidt To: Joel Schopp In-Reply-To: <1264721088.10385.1.camel@jschopp-laptop> References: <1264017638.5717.121.camel@jschopp-laptop> <1264017847.5717.132.camel@jschopp-laptop> <1264548495.12239.56.camel@jschopp-laptop> <1264720855.9660.22.camel@jschopp-laptop> <1264721088.10385.1.camel@jschopp-laptop> Content-Type: text/plain; charset="UTF-8" Date: Fri, 29 Jan 2010 12:23:05 +1100 Message-ID: <1264728185.20211.34.camel@pasglop> Mime-Version: 1.0 Cc: linux-kernel@vger.kernel.org, Ingo Molnar , linuxppc-dev@lists.ozlabs.org, Peter Zijlstra , ego@in.ibm.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2010-01-28 at 17:24 -0600, Joel Schopp wrote: > On Power7 processors running in SMT4 mode with 2, 3, or 4 idle threads > there is performance benefit to idling the higher numbered threads in > the core. > > This patch implements arch_scale_smt_power to dynamically update smt > thread power in these idle cases in order to prefer threads 0,1 over > threads 2,3 within a core. Almost there :-) Joel, Peter, can you help me figure something out tho ? On machine that don't have SMT, I would like to avoid calling arch_scale_smt_power() at all if possible (in addition to not compiling it in if SMT is not enabled in .config). Now, I must say I'm utterly confused by how the domains are setup and I haven't quite managed to sort it out... it looks to me that SD_SHARE_CPUPOWER is always going to be set on all CPUs when the config option is set (though each CPU will have its own domain) or am I misguided ? IE. Is there any sense in having at least a fast exit path out of arch_scale_smt_power() for non-SMT CPUs ? Joel, can you look at compiling it out when SMT is not set ? We don't want to bloat SMP kernels for 32-bit non-SMT embedded platforms. Oh, and one minor nit: > Signed-off-by: Joel Schopp > --- > Version 2 addresses style and optimization, same basic functionality > Version 3 adds a comment, resent due to mailing format error > Index: linux-2.6.git/arch/powerpc/kernel/smp.c > =================================================================== > --- linux-2.6.git.orig/arch/powerpc/kernel/smp.c > +++ linux-2.6.git/arch/powerpc/kernel/smp.c > @@ -620,3 +620,59 @@ void __cpu_die(unsigned int cpu) > smp_ops->cpu_die(cpu); > } > #endif ^^^ Please add the /* CONFIG_CPU_HOTPLUG */ (or whatever it is) that's missing after that #endif :-) Cheers, Ben.