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=-13.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 530C6C49361 for ; Thu, 17 Jun 2021 21:49:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37E4361241 for ; Thu, 17 Jun 2021 21:49:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231398AbhFQVvR (ORCPT ); Thu, 17 Jun 2021 17:51:17 -0400 Received: from linux.microsoft.com ([13.77.154.182]:41018 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231181AbhFQVvQ (ORCPT ); Thu, 17 Jun 2021 17:51:16 -0400 Received: from mail-pf1-f182.google.com (mail-pf1-f182.google.com [209.85.210.182]) by linux.microsoft.com (Postfix) with ESMTPSA id E508420B83FA; Thu, 17 Jun 2021 14:49:07 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com E508420B83FA DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1623966547; bh=iOxmam1hxsYf6Bv7Bb3oOlwGwzgEo/722mgFg6/iGpE=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=ibSIfbBmyJYDw8/UWYKpUQGxmHNuDu0MRvAyGNy+c95/BnDOp7ZTW9zNpKxPLts19 55NTE3ZXCYEnTQtGM6ekpqtH/wNPoAHdCCpkShwRMFY/T9Or3HT+s/tqiH1SqxhxqB h9CoAbLv2b8xsr//Egwd30wlGBPyEax2qpzc4XbU= Received: by mail-pf1-f182.google.com with SMTP id k15so909580pfp.6; Thu, 17 Jun 2021 14:49:07 -0700 (PDT) X-Gm-Message-State: AOAM531a4dNrHsjMuKyEOP/P48vrde16mjYzga9GRW2EVUuD5yMuStaA pbuFrrz1zv3TfpZKdf1z/1eq7YVkIA7OZYZEmVE= X-Google-Smtp-Source: ABdhPJyke/C7KbeDnN/bSq8cETCQLuetyQe+T++OgpvF6JWJDrzSnoEja5DxSnRQ8F98Myf3zBKubi+N4iHqVOpCEZo= X-Received: by 2002:a63:d053:: with SMTP id s19mr6823948pgi.326.1623966547451; Thu, 17 Jun 2021 14:49:07 -0700 (PDT) MIME-Version: 1.0 References: <20210615023812.50885-1-mcroce@linux.microsoft.com> <20210615023812.50885-2-mcroce@linux.microsoft.com> In-Reply-To: From: Matteo Croce Date: Thu, 17 Jun 2021 23:48:31 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/3] riscv: optimized memcpy To: David Laight Cc: Guo Ren , linux-riscv , Linux Kernel Mailing List , linux-arch , Paul Walmsley , Palmer Dabbelt , Albert Ou , Atish Patra , Emil Renner Berthing , Akira Tsukamoto , Drew Fustini , Bin Meng Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 17, 2021 at 11:30 PM David Laight wrote: > > From: Matteo Croce > > Sent: 16 June 2021 19:52 > > To: Guo Ren > > > > On Wed, Jun 16, 2021 at 1:46 PM Guo Ren wrote: > > > > > > Hi Matteo, > > > > > > Have you tried Glibc generic implementation code? > > > ref: https://lore.kernel.org/linux-arch/20190629053641.3iBfk9- > > I_D29cDp9yJnIdIg7oMtHNZlDmhLQPTumhEc@z/#t > > > > > > If Glibc codes have the same performance in your hardware, then you > > > could give a generic implementation first. > > Isn't that a byte copy loop - the performance of that ought to be terrible. > ... > > > I had a look, it seems that it's a C unrolled version with the > > 'register' keyword. > > The same one was already merged in nios2: > > https://elixir.bootlin.com/linux/latest/source/arch/nios2/lib/memcpy.c#L68 > > I know a lot about the nios2 instruction timings. > (I've looked at code execution in the fpga's intel 'logic analiser.) > It is a very simple 4-clock pipeline cpu with a 2-clock delay > before a value read from 'tightly coupled memory' (aka cache) > can be used in another instruction. > There is also a subtle pipeline stall if a read follows a write > to the same memory block because the write is executed one > clock later - and would collide with the read. > Since it only ever executes one instruction per clock loop > unrolling does help - since you never get the loop control 'for free'. > OTOH you don't need to use that many registers. > But an unrolled loop should approach 2 bytes/clock (32bit cpu). > > > I copied _wordcopy_fwd_aligned() from Glibc, and I have a very similar > > result of the other versions: > > > > [ 563.359126] Strings selftest: memcpy(src+7, dst+7): 257 Mb/s > > What clock speed is that running at? > It seems very slow for a 64bit cpu (that isn't an fpga soft-cpu). > > While the small riscv cpu might be similar to the nios2 (and mips > for that matter), there are also bigger/faster cpu. > I'm sure these can execute multiple instructions/clock > and possible even read and write at the same time. > Unless they also support significant instruction re-ordering > the trivial copy loops are going to be slow on such cpu. > It's running at 1 GHz. I get 257 Mb/s with a memcpy, a bit more with a memset, but I get 1200 Mb/s with a cyle which just reads memory with 64 bit addressing. -- per aspera ad upstream