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=unavailable 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 46BCBC5519F for ; Wed, 25 Nov 2020 12:23:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E930B206F7 for ; Wed, 25 Nov 2020 12:22:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727687AbgKYMW7 (ORCPT ); Wed, 25 Nov 2020 07:22:59 -0500 Received: from www62.your-server.de ([213.133.104.62]:56340 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726898AbgKYMW7 (ORCPT ); Wed, 25 Nov 2020 07:22:59 -0500 Received: from sslproxy06.your-server.de ([78.46.172.3]) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1khtoz-0001NT-Gp; Wed, 25 Nov 2020 13:22:53 +0100 Received: from [85.7.101.30] (helo=pc-9.home) by sslproxy06.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1khtoz-0009Ew-Ag; Wed, 25 Nov 2020 13:22:53 +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> <542d88a0-71c0-6d1f-e949-b375d0ac8369@iogearbox.net> From: Daniel Borkmann Message-ID: <43f92e67-b454-b297-4a1d-d61c011a3b3f@iogearbox.net> Date: Wed, 25 Nov 2020 13:22:52 +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 11:09 AM, Magnus Karlsson wrote: > On Wed, Nov 25, 2020 at 11:07 AM Daniel Borkmann wrote: >> >> 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. > > Sounds good. Will do and get back to you. Great, thanks, I took in the current patch to bpf-next in that case and the rest can be followed-up as discussed. Thanks, Daniel