From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-x235.google.com (mail-wr0-x235.google.com [IPv6:2a00:1450:400c:c0c::235]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4090c93nNWzF23j for ; Tue, 27 Mar 2018 03:54:32 +1100 (AEDT) Received: by mail-wr0-x235.google.com with SMTP id m13so6305803wrj.5 for ; Mon, 26 Mar 2018 09:54:32 -0700 (PDT) Date: Mon, 26 Mar 2018 10:54:25 -0600 From: Jason Gunthorpe To: David Laight Cc: 'Benjamin Herrenschmidt' , Sinan Kaya , "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" , Oliver , "linux-rdma@vger.kernel.org" Subject: Re: RFC on writel and writel_relaxed Message-ID: <20180326165425.GA15554@ziepe.ca> References: <3611eabe-2999-1482-b2b4-6d216bbe4762@codeaurora.org> <4e5c745a-8b9b-959e-8893-d99cd6032484@codeaurora.org> <1521692689.16434.293.camel@kernel.crashing.org> <1521726722.16434.312.camel@kernel.crashing.org> <20180323163510.GC13033@ziepe.ca> <1521854626.16434.359.camel@kernel.crashing.org> <58ce5b83f40f4775bec1be8db66adb0d@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <58ce5b83f40f4775bec1be8db66adb0d@AcuMS.aculab.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Mar 26, 2018 at 11:08:45AM +0000, David Laight wrote: > > > This is a super performance critical operation for most drivers and > > > directly impacts network performance. > > Perhaps there ought to be writel_nobarrier() (etc) that never contain > any barriers at all. > This might mean that they are always just the memory operation, > but it would make it more obvious what the driver was doing. I think that is what writel_relaxed is supposed to be. The only restriction it has is that the writes to a single device using UC memory must be kept in program order.. Jason