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Mon, 11 Jun 2018 19:00:04 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w5BJ03RP016138 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 11 Jun 2018 19:00:03 GMT Received: from abhmp0018.oracle.com (abhmp0018.oracle.com [141.146.116.24]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w5BJ02gJ019266; Mon, 11 Jun 2018 19:00:02 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 11 Jun 2018 12:00:02 -0700 Subject: Re: [Xen-devel] [PATCH] xen/netfront: raise max number of slots in xennet_get_responses() To: Juergen Gross , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, netdev@vger.kernel.org Cc: davem@davemloft.net References: <20180611075742.1691-1-jgross@suse.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180611075742.1691-1-jgross@suse.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8921 signatures=668702 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1805220000 definitions=main-1806110213 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/11/2018 03:57 AM, Juergen Gross wrote: > The max number of slots used in xennet_get_responses() is set to > MAX_SKB_FRAGS + (rx->status <= RX_COPY_THRESHOLD). > > In old kernel-xen MAX_SKB_FRAGS was 18, while nowadays it is 17. This > difference is resulting in frequent messages "too many slots" and a > reduced network throughput for some workloads (factor 10 below that of > a kernel-xen based guest). > > Replacing MAX_SKB_FRAGS by XEN_NETIF_NR_SLOTS_MIN for calculation of > the max number of slots to use solves that problem (tests showed no > more messages "too many slots" and throughput was as high as with the > kernel-xen based guest system). > > Signed-off-by: Juergen Gross Reviewed-by: Boris Ostrovsky I wonder also whether netfront_tx_slot_available() is meant to be return (queue->tx.req_prod_pvt - queue->tx.rsp_cons) <                 (NET_TX_RING_SIZE - XEN_NETIF_NR_SLOTS_MIN - 1); which is the same numeric value but provides a more accurate description of what is being tested. -boris > --- > drivers/net/xen-netfront.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c > index 679da1abd73c..ba411005d829 100644 > --- a/drivers/net/xen-netfront.c > +++ b/drivers/net/xen-netfront.c > @@ -790,7 +790,7 @@ static int xennet_get_responses(struct netfront_queue *queue, > RING_IDX cons = queue->rx.rsp_cons; > struct sk_buff *skb = xennet_get_rx_skb(queue, cons); > grant_ref_t ref = xennet_get_rx_ref(queue, cons); > - int max = MAX_SKB_FRAGS + (rx->status <= RX_COPY_THRESHOLD); > + int max = XEN_NETIF_NR_SLOTS_MIN + (rx->status <= RX_COPY_THRESHOLD); > int slots = 1; > int err = 0; > unsigned long ret;