From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 495B2A0093; Thu, 9 Dec 2021 20:43:34 +0100 (CET) Received: from [217.70.189.124] (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 166CD4014F; Thu, 9 Dec 2021 20:43:34 +0100 (CET) Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by mails.dpdk.org (Postfix) with ESMTP id 3DA8240041; Thu, 9 Dec 2021 20:43:32 +0100 (CET) Received: by linux.microsoft.com (Postfix, from userid 1086) id 596E920B7179; Thu, 9 Dec 2021 11:43:31 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 596E920B7179 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1639079011; bh=OZMngE8uO53H7ZSMN2mIQikhOO8juI8WTJUQYPO7U7k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=r4CSsDHlBlxZmHKRqArCBjpySmq3ltx3RelN1t0JZ9vDI775b7+cu4Kb7aU6z1A5k +lHgZ/jtN+vd8ipToJpbEny50VN8iw9TQd2BaMBIByW5ZzQQHJWXyoG8k+08b1v9fw oggjZEdEd/31sCYKa+RoalhFQciMb0cpiwm/bkhc= Date: Thu, 9 Dec 2021 11:43:31 -0800 From: Tyler Retzlaff To: Morten =?iso-8859-1?Q?Br=F8rup?= Cc: "Ananyev, Konstantin" , Thomas Monjalon , "Richardson, Bruce" , techboard@dpdk.org, dev@dpdk.org, Andrew Rybchenko , David Marchand , "Yigit, Ferruh" Subject: Re: [PATCH v1] gpudev: return EINVAL if invalid input pointer for free and unregister Message-ID: <20211209194331.GA26551@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> References: <20211118192802.23955-1-eagostini@nvidia.com> <20211201213749.GA5097@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> <3625450.hdfAi7Kttb@thomas> <98CBD80474FA8B44BF855DF32C47DC35D86D33@smartserver.smartshare.dk> <98CBD80474FA8B44BF855DF32C47DC35D86D34@smartserver.smartshare.dk> <98CBD80474FA8B44BF855DF32C47DC35D86D35@smartserver.smartshare.dk> <20211208173456.GB17852@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> <98CBD80474FA8B44BF855DF32C47DC35D86D4B@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35D86D4B@smartserver.smartshare.dk> User-Agent: Mutt/1.5.21 (2010-09-15) X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On Wed, Dec 08, 2021 at 07:40:10PM +0100, Morten Brørup wrote: > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com] > > Sent: Wednesday, 8 December 2021 18.35 > > > > On Fri, Dec 03, 2021 at 11:37:10AM +0100, Morten Brørup wrote: > > > > From: Morten Brørup [mailto:mb@smartsharesystems.com] > > > > Sent: Thursday, 2 December 2021 14.56 > > > > > > > > > > > > I disagree: Negative value does not mean failure. Only -1 means > > > > failure. > > > > > > > > There is no -2 return value. There is no -EINVAL return value. > > > > > > > > Testing for (ret < 0) might confuse someone to think that other > > values > > > > than -1 could be returned as indication of failure, which is not > > the > > > > case when following the convention where the functions set errno > > and > > > > return -1 in case of failure. > > > > > > > > It would be different if following a convention where the functions > > > > return -errno in case of failure. In this case, testing (ret < 0) > > would > > > > be appropriate. > > > > > > > > So explicitly testing (ret == -1) clarifies which of the two > > > > conventions are relevant. > > > > > > > > > > I tested it on Godbolt, and (ret < 0) produces slightly smaller code > > than (ret == -1) on x86-64: > > > > > > https://godbolt.org/z/3xME3jxq8 > > > > > > A binary test (Error or Data) uses 1 byte less, and a tristate test > > (Error, Zero or Data) uses 3 byte less. > > > > > > Although there is no measurable performance difference for a single > > instance of this kind of test, we should consider that this kind of > > test appears many times in the code, so the saved bytes might add up to > > something slightly significant in the instruction cache. > > > > > > My opinion is not so strong anymore... perhaps we should prefer > > performance over code readability, also in this case? > > > > > > > i would not expect many calls that return rte_errno to be made on the > > hot path. most of the use of errno / rte_errno is control but it's good > > to have considered it. if i start seeing a lot of error handling in hot > > paths i ordinarily find a way to get rid of it through various > > techniques. > > Tyler, I think you and I agree perfectly on this topic. > > -1 should be returned as error, and rte_errno should provide details. > > I'm only saying that comparing the return value with < 0 provides marginally less instruction bytes than comparing it with == -1, so even though -1 is the canonical indication of error, the comparison could be < 0 instead of == -1 (if weighing performance higher than code clarity). sounds about right to me, i appreciate the extra analysis. certainly with explicit -1 it doesn't stop an application gaining the slightly better code generation with < 0. thanks