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 71483467B1; Wed, 21 May 2025 21:39:01 +0200 (CEST) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 63EA842E0C; Wed, 21 May 2025 21:39:01 +0200 (CEST) Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by mails.dpdk.org (Postfix) with ESMTP id 4A10D402CD for ; Wed, 21 May 2025 21:39:00 +0200 (CEST) Received: from mail.maildlp.com (unknown [172.18.186.216]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4b2hSH5QqSz6GDn2; Thu, 22 May 2025 03:34:07 +0800 (CST) Received: from frapeml500008.china.huawei.com (unknown [7.182.85.71]) by mail.maildlp.com (Postfix) with ESMTPS id 977E314020A; Thu, 22 May 2025 03:38:59 +0800 (CST) Received: from frapeml500007.china.huawei.com (7.182.85.172) by frapeml500008.china.huawei.com (7.182.85.71) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Wed, 21 May 2025 21:38:59 +0200 Received: from frapeml500007.china.huawei.com ([7.182.85.172]) by frapeml500007.china.huawei.com ([7.182.85.172]) with mapi id 15.01.2507.039; Wed, 21 May 2025 21:38:59 +0200 From: Konstantin Ananyev To: =?iso-8859-1?Q?Morten_Br=F8rup?= , "dev@dpdk.org" CC: "honnappa.nagarahalli@arm.com" , "jerinj@marvell.com" , "hemant.agrawal@nxp.com" , "drc@linux.ibm.com" Subject: RE: [PATCH v1 1/4] ring: introduce extra run-time checks Thread-Topic: [PATCH v1 1/4] ring: introduce extra run-time checks Thread-Index: AQHbykGpsQqK+1TaqEarZz25/dQkMLPc3a4AgAAkv/CAAGJtoIAAFfLg Date: Wed, 21 May 2025 19:38:59 +0000 Message-ID: <2a514cea0f8f413eba6c85585cc149a9@huawei.com> References: <20250521111432.207936-1-konstantin.ananyev@huawei.com> <20250521111432.207936-2-konstantin.ananyev@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35E9FC7E@smartserver.smartshare.dk> <1e3bcd254b7d4aba8fced00d76b70cee@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35E9FC80@smartserver.smartshare.dk> In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9FC80@smartserver.smartshare.dk> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.171.143] Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 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 > > From: Konstantin Ananyev [mailto:konstantin.ananyev@huawei.com] > > Sent: Wednesday, 21 May 2025 14.35 > > > > > > From: Konstantin Ananyev [mailto:konstantin.ananyev@huawei.com] > > > > Sent: Wednesday, 21 May 2025 13.14 > > > > > > > > Add RTE_ASSERT() to check that different move_tail() flavors > > > > return meaningful *entries value. > > > > It also helps to ensure that inside move_tail(), it uses correct > > > > head/tail values. > > > > > > > > Signed-off-by: Konstantin Ananyev > > > > --- > > > > lib/ring/rte_ring_c11_pvt.h | 2 +- > > > > lib/ring/rte_ring_elem_pvt.h | 8 ++++++-- > > > > lib/ring/rte_ring_hts_elem_pvt.h | 8 ++++++-- > > > > lib/ring/rte_ring_rts_elem_pvt.h | 8 ++++++-- > > > > lib/ring/soring.c | 2 ++ > > > > 5 files changed, 21 insertions(+), 7 deletions(-) > > > > > > > > diff --git a/lib/ring/rte_ring_c11_pvt.h > > b/lib/ring/rte_ring_c11_pvt.h > > > > index b9388af0da..0845cd6dcf 100644 > > > > --- a/lib/ring/rte_ring_c11_pvt.h > > > > +++ b/lib/ring/rte_ring_c11_pvt.h > > > > @@ -104,10 +104,10 @@ __rte_ring_headtail_move_head(struct > > > > rte_ring_headtail *d, > > > > n =3D (behavior =3D=3D RTE_RING_QUEUE_FIXED) ? > > > > 0 : *entries; > > > > > > > > + *new_head =3D *old_head + n; > > > > if (n =3D=3D 0) > > > > return 0; > > > > > > > > - *new_head =3D *old_head + n; > > > > if (is_st) { > > > > d->head =3D *new_head; > > > > success =3D 1; > > > > > > Is there a need to assign a value to *new_head if n=3D=3D0? > > > > Not really, main reason I just moved this line up - to keep compiler > > happy. > > Otherwise it complained that *new_head might be left uninitialized. >=20 > Your change might give the impression that *new_head is used by a caller.= (Like I asked about.) > To please the compiler, you could mark new_head __rte_unused, or: >=20 > - if (n =3D=3D 0) > + if (n =3D=3D 0) { > + RTE_SET_USED(new_head); > return 0; > + } >=20 > > Makes sense, will re-spin. Do you have any comments for other patches in the series? Thanks Konstantin=20 > > > I don't think your suggestion is multi-thread safe. > > > If d->head moves, the value in *new_head will be incorrect. > > > > If d->head moves, then *old_head will also be incorrect. > > For that case we do have CAS() below, it will return zero if (d->head > > !=3D *old_head) > > and we shall go to the next iteration (attempt). >=20 > Exactly. > And with my suggestion the same will happen if n=3D=3D0, and the next att= empt will update them both, until they are both correct. >=20 > > Basically - if n =3D=3D 0, your *old_head and *new_head might be invali= d > > and should not be used > > (and they are not used). > > > > > Instead, suggest: > > > > > > - if (n =3D=3D 0) > > > - return 0; > > > > > > *new_head =3D *old_head + n; > > > if (is_st) { > > > d->head =3D *new_head; > > > success =3D 1; > > > } else > > > /* on failure, *old_head is updated */ > > > success =3D > > rte_atomic_compare_exchange_strong_explicit( > > > &d->head, old_head, *new_head, > > > rte_memory_order_relaxed, > > > rte_memory_order_relaxed); > > > } while (unlikely(success =3D=3D 0)); > > > > That's possible, but if (n =3D=3D0) we probably don't want to update th= e > > head - > > as we are not moving head - it is pointless, while still expensive. >=20 > Agree. Let's avoid unnecessary cost! > My suggestion was only relevant if *new_head needed to be updated when n= =3D=3D0. >=20