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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 C8919C282DA for ; Tue, 9 Apr 2019 09:11:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A31C320651 for ; Tue, 9 Apr 2019 09:11:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726372AbfDIJLH (ORCPT ); Tue, 9 Apr 2019 05:11:07 -0400 Received: from www62.your-server.de ([213.133.104.62]:57588 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726079AbfDIJLG (ORCPT ); Tue, 9 Apr 2019 05:11:06 -0400 Received: from [78.46.172.2] (helo=sslproxy05.your-server.de) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1hDmmS-00074t-Rm; Tue, 09 Apr 2019 11:11:00 +0200 Received: from [178.197.248.24] (helo=linux.home) by sslproxy05.your-server.de with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1hDmmS-000Kh5-IF; Tue, 09 Apr 2019 11:11:00 +0200 Subject: Re: [PATCH bpf 2/2] libbpf: remove dependency on barrier.h in xsk.h To: Magnus Karlsson , bjorn.topel@intel.com, ast@kernel.org, netdev@vger.kernel.org Cc: bpf@vger.kernel.org, bruce.richardson@intel.com, ciara.loftus@intel.com, ilias.apalodimas@linaro.org, xiaolong.ye@intel.com, ferruh.yigit@intel.com, qi.z.zhang@intel.com, georgmueller@gmx.net, will.deacon@arm.com References: <1554792253-27081-1-git-send-email-magnus.karlsson@intel.com> <1554792253-27081-3-git-send-email-magnus.karlsson@intel.com> From: Daniel Borkmann Message-ID: <621a9d70-5397-da90-a68c-6f12f5cbd3b2@iogearbox.net> Date: Tue, 9 Apr 2019 11:10:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <1554792253-27081-3-git-send-email-magnus.karlsson@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.100.3/25414/Tue Apr 9 09:53:33 2019) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 04/09/2019 08:44 AM, Magnus Karlsson wrote: > The use of smp_rmb() and smp_wmb() creates a Linux header dependency > on barrier.h that is uneccessary in most parts. This patch implements > the two small defines that are needed from barrier.h. As a bonus, the > new implementations are faster than the default ones as they default > to sfence and lfence for x86, while we only need a compiler barrier in > our case. Just as it is when the same ring access code is compiled in > the kernel. > > Fixes: 1cad07884239 ("libbpf: add support for using AF_XDP sockets") > Signed-off-by: Magnus Karlsson > --- > tools/lib/bpf/xsk.h | 19 +++++++++++++++++-- > 1 file changed, 17 insertions(+), 2 deletions(-) > > diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h > index 3638147..317b44f 100644 > --- a/tools/lib/bpf/xsk.h > +++ b/tools/lib/bpf/xsk.h > @@ -39,6 +39,21 @@ DEFINE_XSK_RING(xsk_ring_cons); > struct xsk_umem; > struct xsk_socket; > > +#if !defined bpf_smp_rmb && !defined bpf_smp_wmb > +# if defined(__i386__) || defined(__x86_64__) > +# define bpf_smp_rmb() asm volatile("" : : : "memory") > +# define bpf_smp_wmb() asm volatile("" : : : "memory") > +# elif defined(__aarch64__) > +# define bpf_smp_rmb() asm volatile("dmb ishld" : : : "memory") > +# define bpf_smp_wmb() asm volatile("dmb ishst" : : : "memory") > +# elif defined(__arm__) > +# define bpf_smp_rmb() asm volatile("dmb ish" : : : "memory") > +# define bpf_smp_wmb() asm volatile("dmb ishst" : : : "memory") > +# else > +# error Architecture not supported by the XDP socket code in libbpf. > +# endif > +#endif Hmm, bit unfortunate, but I can see why it's needed inside the header here as it's installed into the system and needs to be included by applications. Fine with me. In any case, I still think we should also fix it for tooling infra to avoid others running into the same issue, lemme resurrect [0] from back in the days. One question though regarding above arm32 implementation. You match these barriers against the ones from af_xdp in kernel. So smp_* variants from the arch/arm/include/asm/barrier.h header need to be matched. This selects the dmb(ish) and dmb(ishst) variant. The implementation of dmb() however is quite CPU dependent, the above assumes to match with __LINUX_ARM_ARCH__ >= 7. Perhaps this assumption needs at minimum a comment to make it clear for developers. [0] https://lore.kernel.org/netdev/20181017144156.16639-2-daniel@iogearbox.net/ > static inline __u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill, > __u32 idx) > { > @@ -119,7 +134,7 @@ static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb) > /* Make sure everything has been written to the ring before signalling > * this to the kernel. > */ > - smp_wmb(); > + bpf_smp_wmb(); > > *prod->producer += nb; > } > @@ -133,7 +148,7 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, > /* Make sure we do not speculatively read the data before > * we have received the packet buffers from the ring. > */ > - smp_rmb(); > + bpf_smp_rmb(); > > *idx = cons->cached_cons; > cons->cached_cons += entries; >