Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753733Ab1DOXZL (ORCPT ); Fri, 15 Apr 2011 19:25:11 -0400 Received: from mail-yx0-f174.google.com ([209.85.213.174]:62744 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751314Ab1DOXZJ convert rfc822-to-8bit (ORCPT ); Fri, 15 Apr 2011 19:25:09 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=j8mMknjI0bEYDrD1BtdmhgOQCjmLJHXTglwqmPBxqTs3rFm35lL1G6wPSfatsnrBo2 fi18ht1T/fEHRTTIYXj7Q9WcrYCumuEP196FiOmH4JIac+VmGZw25+eAl/iScptKvAnF F7rLOAa7SbsOQvIBoVlu66FKYf5tob0bIoX/Q= MIME-Version: 1.0 In-Reply-To: <201104160111.49409.rjw@sisk.pl> References: <20110415162938.GA11454@atrey.karlin.mff.cuni.cz> <201104160111.49409.rjw@sisk.pl> From: Mike Frysinger Date: Fri, 15 Apr 2011 19:24:47 -0400 X-Google-Sender-Auth: HB7kUYyx_Ri6BmZ1t83aVodcrhs Message-ID: Subject: Re: [uclinux-dist-devel] [linux-pm] freezer: should barriers be smp ? To: "Rafael J. Wysocki" Cc: Pavel Machek , Alan Stern , uclinux-dist-devel@blackfin.uclinux.org, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1891 Lines: 43 On Fri, Apr 15, 2011 at 19:11, Rafael J. Wysocki wrote: > On Friday, April 15, 2011, Mike Frysinger wrote: >> On Fri, Apr 15, 2011 at 12:29, Pavel Machek wrote: >> >> > > I believe the code is correct as is. >> >> > >> >> > that isnt what the code / documentation says.  unless i'm reading them >> >> > wrong, both seem to indicate that the proposed patch is what we >> >> > actually want. >> >> >> >> The existing code is correct but it isn't optimal. >> >> >> >> wmb() and rmb() are heavy-duty operations, and you don't want to call >> >> them when they aren't needed.  That's exactly what smp_wmb() and >> >> smp_rmb() are for -- they call wmb() and rmb(), but only in SMP >> >> kernels. >> >> >> >> Unless you need to synchronize with another processor (not necessarily >> >> a CPU, it could be something embedded within a device), you should >> >> always use smp_wmb() and smp_rmb() rather than wmb() and rmb(). >> > >> > Maybe; but this code is not performance critical and I believe being >> > obvious here is better... >> >> isnt it though ?  especially when we talk about suspending/resuming on >> embedded systems to get more savings over just cpu idle ?  we want >> that latency to be as low as possible. > > I agree, we can switch the freezer to smp_ barriers, but not for the reason > you gave before. :-) > > Care to repost the patch with a suitable changelog? np to be clear, what you said wrt the Blackfin smp barriers still holds true right ? so this changset i merged doesnt need any tweaking ... http://git.kernel.org/?p=linux/kernel/git/vapier/blackfin.git;a=commitdiff;h=943aee0c685d0563228d5a2ad9c8394ad0300fb5 -mike -- 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/