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 C9F64A0C41; Wed, 23 Jun 2021 16:11:44 +0200 (CEST) Received: from [217.70.189.124] (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id B18B94003F; Wed, 23 Jun 2021 16:11:44 +0200 (CEST) Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by mails.dpdk.org (Postfix) with ESMTP id 317BA4003E; Wed, 23 Jun 2021 16:11:43 +0200 (CEST) IronPort-SDR: jZlqSTEZ/gfnCqBGGcEYQcpiMtOw3+ZKZNuFgHvRDHcwOTDLpgsMquTcB387HWsrfhR7m2b90C t4dDIisrYyJA== X-IronPort-AV: E=McAfee;i="6200,9189,10024"; a="204261030" X-IronPort-AV: E=Sophos;i="5.83,294,1616482800"; d="scan'208";a="204261030" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Jun 2021 07:11:39 -0700 IronPort-SDR: zd+5Z6h7g25BffEzDsldYEkOTKqYfa/JoY8iAJB/NbNQ2Sscu9CLi7mpE839NOEDSfdXUIsVWf e0S27dTD4dww== X-IronPort-AV: E=Sophos;i="5.83,294,1616482800"; d="scan'208";a="453049331" Received: from fyigit-mobl1.ger.corp.intel.com (HELO [10.213.219.144]) ([10.213.219.144]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Jun 2021 07:11:36 -0700 To: wangyunjian , Thomas Monjalon Cc: "dev@dpdk.org" , "stable@dpdk.org" , "gowrishankar.m@linux.vnet.ibm.com" , dingxiaoxiong , "liucheng (J)" References: <4aebf99afe5bae2b25f2e5445a32243ffd6f7e97.1624359204.git.wangyunjian@huawei.com> <1624365869-31872-1-git-send-email-wangyunjian@huawei.com> <3564511.TeOt0uO2Lr@thomas> From: Ferruh Yigit X-User: ferruhy Message-ID: <8b7084b2-12fc-acd6-9cf8-1bc238b77d7d@intel.com> Date: Wed, 23 Jun 2021 15:11:33 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [dpdk-stable] [PATCH v3] kni: fix mbuf allocation for alloc FIFO 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 Sender: "dev" On 6/23/2021 1:16 PM, wangyunjian wrote: > > >> -----Original Message----- >> From: Thomas Monjalon [mailto:thomas@monjalon.net] >> Sent: Wednesday, June 23, 2021 4:46 AM >> To: wangyunjian ; liucheng (J) >> >> Cc: dev@dpdk.org; stable@dpdk.org; ferruh.yigit@intel.com; >> gowrishankar.m@linux.vnet.ibm.com; dingxiaoxiong >> ; wangyunjian >> Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v3] kni: fix mbuf allocation for alloc >> FIFO >> >> 22/06/2021 14:44, wangyunjian: >>> From: Yunjian Wang >>> >>> In kni_allocate_mbufs(), we alloc mbuf for alloc_q as this code. >>> allocq_free = (kni->alloc_q->read - kni->alloc_q->write - 1) \ >>> & (MAX_MBUF_BURST_NUM - 1); >>> The value of allocq_free maybe zero, for example : >>> The ring size is 1024. After init, write = read = 0. Then we fill >>> kni->alloc_q to full. At this time, write = 1023, read = 0. >>> >>> Then the kernel send 32 packets to userspace. At this time, write = >>> 1023, read = 32. And then the userspace receive this 32 packets. >>> Then fill the kni->alloc_q, (32 - 1023 - 1) & 31 = 0, fill nothing. >>> ... >>> Then the kernel send 32 packets to userspace. At this time, write = >>> 1023, read = 992. And then the userspace receive this 32 packets. >>> Then fill the kni->alloc_q, (992 - 1023 - 1) & 31 = 0, fill nothing. >>> >>> Then the kernel send 32 packets to userspace. The kni->alloc_q only >>> has 31 mbufs and will drop one packet. >>> >>> Absolutely, this is a special scene. Normally, it will fill some mbufs >>> everytime, but may not enough for the kernel to use. >>> >>> In this patch, we always keep the kni->alloc_q to full for the kernel >>> to use. >>> >>> Fixes: 49da4e82cf94 ("kni: allocate no more mbuf than empty slots in >>> queue") >>> Cc: stable@dpdk.org >>> >>> Signed-off-by: Cheng Liu >>> Signed-off-by: Yunjian Wang >>> Acked-by: Ferruh Yigit >>> --- >>> v3: >>> update patch title >>> v2: >>> add fixes tag and update commit log >>> --- >>> lib/kni/rte_kni.c | 5 +++-- >>> 1 file changed, 3 insertions(+), 2 deletions(-) >>> >>> diff --git a/lib/kni/rte_kni.c b/lib/kni/rte_kni.c index >>> 9dae6a8d7c..eb24b0d0ae 100644 >>> --- a/lib/kni/rte_kni.c >>> +++ b/lib/kni/rte_kni.c >>> @@ -677,8 +677,9 @@ kni_allocate_mbufs(struct rte_kni *kni) >>> return; >>> } >>> >>> - allocq_free = (kni->alloc_q->read - kni->alloc_q->write - 1) >>> - & (MAX_MBUF_BURST_NUM - 1); >>> + allocq_free = kni_fifo_free_count(kni->alloc_q); >> >> Can we insert a comment here to explain the logic? > > OK, how about like this? > > /* Because 'read/write' maybe not volatile, so use kni_fifo_free_count() > * to get the num of available elements in the fifo > */ > A comment like above may make sense in the commit log to explain the reason of the change, but for developer reading the new code it doesn't give any useful information, it even may be confusing. @Thomas, Code gets the numbers of the free slots in the FIFO and fills it up to MAX_NUM unless it gets full first. Can you please clarify which logic to comment more? >> >>> + allocq_free = (allocq_free > MAX_MBUF_BURST_NUM) ? >>> + MAX_MBUF_BURST_NUM : allocq_free; >>> for (i = 0; i < allocq_free; i++) { >>> pkts[i] = rte_pktmbuf_alloc(kni->pktmbuf_pool); >>> if (unlikely(pkts[i] == NULL)) { >> >> About the title, I don't understand the part "for alloc FIFO", given all mbufs are >> in a FIFO queue in KNI, right? > > The title is "kni: fix mbuf allocation for FIFO queue"? > There are multiple FIFOs in the KNI, one of their name is 'alloc_q', which is for providing mbufs to the kernel side to use. So userspace allocates mbufs and puts them to 'alloc_q' to be used by kernel side. Mainly the "kni: fix mbuf allocation" is enough to describe the fix, but it sounds too generic, "for alloc FIFO" gives more context to clarify which mbuf allocation we are referring too. It is also possible to say as below without refering to name of the FIFO: "kni: fix mbuf allocation for kernel side use" Is this any better?