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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 D6F5BC433DF for ; Sat, 4 Jul 2020 12:09:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAB6D20890 for ; Sat, 4 Jul 2020 12:09:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593864581; bh=X22tQmeMJ8J3B60hTKOzNA4Xdp+LVatGyVDda2h5yfI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=eVKzfErjFntj9GBJRH6v3BK/WNrOiZSK9rL7xNczRAZQEiyIiuUkDd75Ppan8qjT7 lnLL/Z/Rp1C8vzV05spn5LNsLdWRY9CrwSj1VFZSaU6AGs4TJ9O8XPv802X1rc1m96 zLOXLQ8C7AvMKXF/i3Ci1PZRd3qKbjhuzHghb5V0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727090AbgGDMJk (ORCPT ); Sat, 4 Jul 2020 08:09:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:57182 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726621AbgGDMJj (ORCPT ); Sat, 4 Jul 2020 08:09:39 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1F26C20885; Sat, 4 Jul 2020 12:09:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593864579; bh=X22tQmeMJ8J3B60hTKOzNA4Xdp+LVatGyVDda2h5yfI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=esjXWAn/cWRcpXzz410rtEMYcAQdEn8CFgrY8KAcQghAJyp2xZjohPVYbxTlJp7Ou l+ROhInoynGXtle7oWOE61SUDm34ZjtXWXHDFlDeThvaeUr9ErOrr1tmrW+uSgZd1p c44hkrUSNW/tEjp4YaNrlG4n7U80WqNuRlZxBRZ0= Date: Sat, 4 Jul 2020 13:09:34 +0100 From: Will Deacon To: Saravana Kannan Cc: Ard Biesheuvel , Catalin Marinas , Android Kernel Team , linux-arm-kernel , Linux Kernel Mailing List Subject: Re: [PATCH v2] arm64/module: Optimize module load time by optimizing PLT counting Message-ID: <20200704120934.GA21097@willie-the-truck> References: <20200623011803.91232-1-saravanak@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 03, 2020 at 05:47:24PM -0700, Saravana Kannan wrote: > On Thu, Jul 2, 2020 at 8:30 AM Ard Biesheuvel wrote: > > On Tue, 23 Jun 2020 at 03:27, Saravana Kannan wrote: > > > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > > > index 65b08a74aec6..0ce3a28e3347 100644 > > > --- a/arch/arm64/kernel/module-plts.c > > > +++ b/arch/arm64/kernel/module-plts.c > > > @@ -253,6 +253,40 @@ static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num, > > > return ret; > > > } > > > > > > +static bool branch_rela_needs_plt(Elf64_Sym *syms, Elf64_Rela *rela, > > > + Elf64_Word dstidx) > > > +{ > > > + > > > + Elf64_Sym *s = syms + ELF64_R_SYM(rela->r_info); > > > + > > > + if (s->st_shndx == dstidx) > > > + return false; > > > + > > > + return ELF64_R_TYPE(rela->r_info) == R_AARCH64_JUMP26 || > > > + ELF64_R_TYPE(rela->r_info) == R_AARCH64_CALL26; > > > +} > > > + > > > +/* Group branch PLT relas at the front end of the array. */ > > > +static int partition_branch_plt_relas(Elf64_Sym *syms, Elf64_Rela *rela, > > > + int numrels, Elf64_Word dstidx) > > > +{ > > > + int i = 0, j = numrels - 1; > > > + > > > + if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) > > > + return 0; > > > + > > > + while (i < j) { > > > + if (branch_rela_needs_plt(syms, &rela[i], dstidx)) > > > + i++; > > > + else if (branch_rela_needs_plt(syms, &rela[j], dstidx)) > > > + swap(rela[i], rela[j]); > > > > Nit: would be slightly better to put > > > > swap(rela[i++], rela[j]); > > > > here so the next iteration of the loop will not call > > branch_rela_needs_plt() on rela[i] redundantly. But the current code > > is also correct. > > Oh yeah, I noticed that unnecessary repeat of branch_rela_needs_plt() > on rela[i] when j had to be decremented, but forgot to handle it after > I was done with all the testing. Yeah, I guess you can decrement j as well, but I just think it makes the logic harder to read and more error-prone if we change it later. > But I did compare it to the code I had written in v1 that didn't have > this extra check for rela[i]. I couldn't find any measurable > difference in the module load time. Maybe 1ms for the worst case > module, but that could have been just run to run variation. > > Anyway, maybe send this as another patch since Catalin has already > picked this mine? I think the queued code is fine, so we don't need to micro-optimise it. Will