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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 3D1C2C6379D for ; Wed, 25 Nov 2020 10:07:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E244420872 for ; Wed, 25 Nov 2020 10:07:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728808AbgKYKHE (ORCPT ); Wed, 25 Nov 2020 05:07:04 -0500 Received: from www62.your-server.de ([213.133.104.62]:60964 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726124AbgKYKHE (ORCPT ); Wed, 25 Nov 2020 05:07:04 -0500 Received: from sslproxy03.your-server.de ([88.198.220.132]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1khrhT-00035U-Am; Wed, 25 Nov 2020 11:06:59 +0100 Received: from [85.7.101.30] (helo=pc-9.home) by sslproxy03.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1khrhT-000Fbj-4f; Wed, 25 Nov 2020 11:06:59 +0100 Subject: Re: [PATCH][V2] libbpf: add support for canceling cached_cons advance To: Magnus Karlsson Cc: Li RongQing , Network Development , bpf , "Karlsson, Magnus" References: <1606202474-8119-1-git-send-email-lirongqing@baidu.com> From: Daniel Borkmann Message-ID: <542d88a0-71c0-6d1f-e949-b375d0ac8369@iogearbox.net> Date: Wed, 25 Nov 2020 11:06:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.4/25998/Tue Nov 24 14:16:50 2020) Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 11/25/20 10:13 AM, Magnus Karlsson wrote: > On Wed, Nov 25, 2020 at 10:02 AM Daniel Borkmann wrote: >> On 11/25/20 9:30 AM, Magnus Karlsson wrote: >>> On Tue, Nov 24, 2020 at 10:58 PM Daniel Borkmann wrote: >>>> On 11/24/20 9:12 AM, Magnus Karlsson wrote: >>>>> On Tue, Nov 24, 2020 at 8:33 AM Li RongQing wrote: >>>>>> >>>>>> Add a new function for returning descriptors the user received >>>>>> after an xsk_ring_cons__peek call. After the application has >>>>>> gotten a number of descriptors from a ring, it might not be able >>>>>> to or want to process them all for various reasons. Therefore, >>>>>> it would be useful to have an interface for returning or >>>>>> cancelling a number of them so that they are returned to the ring. >>>>>> >>>>>> This patch adds a new function called xsk_ring_cons__cancel that >>>>>> performs this operation on nb descriptors counted from the end of >>>>>> the batch of descriptors that was received through the peek call. >>>>>> >>>>>> Signed-off-by: Li RongQing >>>>>> [ Magnus Karlsson: rewrote changelog ] >>>>>> Cc: Magnus Karlsson >>>>>> --- >>>>>> diff with v1: fix the building, and rewrote changelog >>>>>> >>>>>> tools/lib/bpf/xsk.h | 6 ++++++ >>>>>> 1 file changed, 6 insertions(+) >>>>>> >>>>>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h >>>>>> index 1069c46364ff..1719a327e5f9 100644 >>>>>> --- a/tools/lib/bpf/xsk.h >>>>>> +++ b/tools/lib/bpf/xsk.h >>>>>> @@ -153,6 +153,12 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, >>>>>> return entries; >>>>>> } >>>>>> >>>>>> +static inline void xsk_ring_cons__cancel(struct xsk_ring_cons *cons, >>>>>> + size_t nb) >>>>>> +{ >>>>>> + cons->cached_cons -= nb; >>>>>> +} >>>>>> + >>>>>> static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb) >>>>>> { >>>>>> /* Make sure data has been read before indicating we are done >>>>>> -- >>>>>> 2.17.3 >>>>> >>>>> Thank you RongQing. >>>>> >>>>> Acked-by: Magnus Karlsson >>>> >>>> @Magnus: shouldn't the xsk_ring_cons__cancel() nb type be '__u32 nb' instead? >>> >>> All the other interfaces have size_t as the type for "nb". It is kind >>> of weird as a __u32 would have made more sense, but cannot actually >>> remember why I chose a size_t two years ago. But for consistency with >>> the other interfaces, let us keep it a size_t for now. I will do some >>> research around the reason. >> >> It's actually a bit of a mix currently which is what got me confused: >> >> static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb) >> static inline __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb) >> static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx) >> static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb) >> static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx) >> static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb) >> >> (I can take it in as-is, but would be nice to clean it up a bit to avoid confusion.) > > Hmm, that is confusing indeed. Well, the best choice would be __u32 > everywhere since the ring pointers themselves are __u32. But I am > somewhat afraid of changing an API. Can we guarantee that a change > from size_t to __u32 will not break some user's compilation? Another > option would be to clean this up next year when we will very likely > produce a 1.0 version of this API and at that point we can change some > things. What do you think would be the best approach? Given they're all inlines, imho, risk should be fairly low to switch all to __u32. I would probably go and verify first with DPDK as main user of the lib and/or write some test cases to see if compiler spills any new warnings and the like, but if not the case then we should do it for bpf-next so this has plenty of exposure in the meantime. Any nb large than u32 max is a bug in any case. Thanks, Daniel