From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1254C433FE for ; Fri, 10 Sep 2021 13:33:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86A4B61167 for ; Fri, 10 Sep 2021 13:33:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233522AbhIJNet (ORCPT ); Fri, 10 Sep 2021 09:34:49 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:23210 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233230AbhIJNes (ORCPT ); Fri, 10 Sep 2021 09:34:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631280817; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=N7xXcGHMUs/Wg9j2dc3lT0r3M8QRHdv0xEqXqfTyuuw=; b=E0/Lm2Y6O8QchfNo+L+TO+99m9U3k4Hz78UhQerzBs8CApS1tXpM/DDNtmydNbdaOTUEAA o0s7C/Zhe4M7uYU6yv57Jmc+m1JM7ouNu+2DkIwqqR7kLF67k6xgmpFgOwqnXe9yFTgPyy ALyoA8G09MOxbZTH/u75Q17W3ZQPzaw= Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-402-5NVFBT8aMLKxIifMrQUbzQ-1; Fri, 10 Sep 2021 09:33:07 -0400 X-MC-Unique: 5NVFBT8aMLKxIifMrQUbzQ-1 Received: by mail-io1-f71.google.com with SMTP id g2-20020a6b7602000000b005be59530196so2740692iom.0 for ; Fri, 10 Sep 2021 06:33:07 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=N7xXcGHMUs/Wg9j2dc3lT0r3M8QRHdv0xEqXqfTyuuw=; b=V3oG0GHCeUl8oTNvhlnXIWo/PrvqIV3aGtZ2cKheS8AVzjhX2kLfcxzTpxgqgp+msy j0rwxHIdsP1jwrQBccryrnXrKk0CTC/2/KBr7QJZ05rsiqTac3ikytgdZTRMpI3PODqh SfS4+rN2Qs2QLm24wd03DceQlILdQiMNKgAH+9u9dYufMxtF40QJxu5o47eMlrEgOPnx bhr9vPKSnY5/DLM3ZgcMC1W4AOQb7e8yBoLlaVwLEsB1JIxEnAJXEv322N0XxVMhrZpR vyDdKjeZR+9T062nOR7XyQfsxSTNDFTRh7RYNMZQGC9/kcVyWs5dw23b0OhbAu9CFwEp MT5Q== X-Gm-Message-State: AOAM530oTYYLncMXKseQQdz5Vv5v9XqxuCtxop9AJlT3b269RDbB1iVa iR862Ndd01w2o5ky8LR233oZ4llyUafgwCIeYewDlpzXq1eofcvmw6Hlkvyp/9OZMZtaR5PZHw/ vsVPQVv+amAAFjPSVYwm+2KP39Wg= X-Received: by 2002:a05:6638:419e:: with SMTP id az30mr4548911jab.90.1631280787235; Fri, 10 Sep 2021 06:33:07 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzhNGhQWPKFaAbGzzt0JTb2OdDw4GQ74T8lw4HZJb7E7+uD7XlttVoci/4/ZRDlfdB3p/55xw== X-Received: by 2002:a05:6638:419e:: with SMTP id az30mr4548897jab.90.1631280786984; Fri, 10 Sep 2021 06:33:06 -0700 (PDT) Received: from t490s ([2607:fea8:56a2:9100::d35a]) by smtp.gmail.com with ESMTPSA id r18sm2506680ioa.13.2021.09.10.06.33.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Sep 2021 06:33:06 -0700 (PDT) Date: Fri, 10 Sep 2021 09:33:04 -0400 From: Peter Xu To: nsaenzju@redhat.com Cc: linux-rt-users@vger.kernel.org, williams@redhat.com, jkacur@redhat.com Subject: Re: [PATCH 2/3] oslat: Add aarch64 support Message-ID: References: <20210908100209.118609-1-nsaenzju@redhat.com> <20210908100209.118609-2-nsaenzju@redhat.com> <466f7d726df2dfec8ac83a9d3f603439e3cec1b1.camel@redhat.com> <6a2eba408dc4260a47c1acfe743474bb39aa93bd.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6a2eba408dc4260a47c1acfe743474bb39aa93bd.camel@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Fri, Sep 10, 2021 at 02:19:40PM +0200, nsaenzju@redhat.com wrote: > > I also don't understand why you explicitly removed the compiler barrier. IIUC > > when without it the compiler could move these instructions to be before/after > > other instructions generated in the c code. That may not really happen in > > practise, but just curious why the explicit removal. > > I removed it too as I see no justification for it. There is nothing, except for > the actual timestamp values (which are safe as they come from an mrs), that > could suffer from the compiler prefetching the value, or reordering accesses. > I'll add a comment on the commit message. Again I have no solid example, but wondering whether when without compiler barrier the compiler would be legal to compile this code clip: t1 = frc(); a = 1; t2 = frc(); into something like: t1 = frc(); t2 = frc(); a = 1; It's just that iiuc compiler barrier has 0 overhead to us. No strong opinion anyways. -- Peter Xu