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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 73A06C433ED for ; Thu, 1 Apr 2021 14:28:07 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 388096128D for ; Thu, 1 Apr 2021 14:28:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 388096128D Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.104551.200088 (Exim 4.92) (envelope-from ) id 1lRyId-0004R3-4m; Thu, 01 Apr 2021 14:27:55 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 104551.200088; Thu, 01 Apr 2021 14:27:55 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lRyId-0004Qw-1K; Thu, 01 Apr 2021 14:27:55 +0000 Received: by outflank-mailman (input) for mailman id 104551; Thu, 01 Apr 2021 14:27:53 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lRyIb-0004Qq-HA for xen-devel@lists.xenproject.org; Thu, 01 Apr 2021 14:27:53 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 6abfc8e0-307b-48a0-8f78-f7d7717b2082; Thu, 01 Apr 2021 14:27:52 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9CFFEB1BC; Thu, 1 Apr 2021 14:27:51 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 6abfc8e0-307b-48a0-8f78-f7d7717b2082 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617287271; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=uqjRHjMJw8JbA2dlMGmgldrt6ty/trqzJ0kd0jTS3x0=; b=T6OHUx5p4RbTA9CYGUOWblyujMjReWbQ0qY2dzRovS2e9vKkFK2OgTk2yLQNg8i9iKwK5N v4Pn3LeN8YcI6VX8SeV2py/tn7eJWdebUY9nQTBDVsc0PiVHIBGyXuiSt3bYVJZImsd3ax bUvpux0c5QaMfyh8VyHOoj7Xn9jp/1A= Subject: Re: [PATCH 00/23] further population of xen/lib/ To: Julien Grall Cc: Andrew Cooper , George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu , "xen-devel@lists.xenproject.org" References: <27916fa0-9ebd-a49a-bbb9-1ef47c2b5bf6@xen.org> <4f745d03-baa8-e9e6-692c-f9c9f401b766@suse.com> <6a38f0db-938b-fd13-48e6-6b538c85fe42@xen.org> From: Jan Beulich Message-ID: Date: Thu, 1 Apr 2021 16:27:50 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <6a38f0db-938b-fd13-48e6-6b538c85fe42@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 01.04.2021 16:04, Julien Grall wrote: > Hi Jan, > > On 01/04/2021 14:43, Jan Beulich wrote: >> On 01.04.2021 13:54, Julien Grall wrote: >>> On 01/04/2021 11:14, Jan Beulich wrote: >>>> This is to dissolve / move xen/common/lib.c and xen/common/string.c. >>>> One benefit of moving these functions into an archive is that we can >>>> drop some of the related __HAVE_ARCH_* #define-s: By living in an >>>> archive, the per-arch functions will preempt any loading of the >>>> respective functions (objects) from the archive. (Down the road we >>>> may want to move the per-arch functions into archives as well, at >>>> which point the per-arch archive(s) would need to be specified ahead >>>> of the common one(s) to the linker.) >>> >>> While I think it is a good idea to move code in xen/lib, I am not >>> convinced that having a single function per file is that beneficial. >>> >>> Do you have numbers showing how much Xen will shrink after this series? >> >> In the default build, from all I was able to tell, there's one function >> that's unused (strspn(), as mentioned in the respective patch description). >> I don't think I've been claiming any space savings here, though, so I > > You didn't. I was trying to guess why you wrote this series given that > your cover letter doesn't provide a lot of benefits (other than dropping > __HAVE_ARCH_*). > >> wonder why you make this a criteria at all. > > Because this is the main reason I would be willing to ack this series. > This outweight the increase number of files with just a single function > implemented. > >> The functions being one per >> CU is such that they can be individually overridden by an arch, without >> pulling in dead code. > > I would agree with functions like memcpy/memset() because you can gain a > lot to outweight the implementation in assembly. I am not convinced this > would be true for functions such as strlen(). strlen() is actually a pretty good candidate for overriding, and we may even want to on x86 with newer hardware's "Fast Short REP CMPSB/SCASB". > So overall, the number of functions requiring overriding will likely be > pretty limited and #ifdef would be IMHO tolerable. > > Although, I would be OK with creating a file per function that are > already overrided. For all the others, I think this is just pointless. Well, I don't see a reason to special case individual functions. Plus any reasonable static library should imo have one (global) function per object file in the normal case; there may be very few exceptions. Drawing an ad hoc boundary at what currently has an override somewhere doesn't look very attractive to me. Plus to be honest while I would find it unfair to ask to further split things if I did just a partial conversion (i.e. invest yet more time), I find it rather odd to be asked to undo some of the splitting when I've already taken the extra time to make things consistent. Jan