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Thu, 8 Sep 2022 09:40:27 +0000 (GMT) Received: from [9.171.66.190] (unknown [9.171.66.190]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 8 Sep 2022 09:40:27 +0000 (GMT) Message-ID: <375efe42-910d-69ae-e48d-cff0298dd104@linux.ibm.com> Date: Thu, 8 Sep 2022 11:40:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [RFC net] tcp: Fix performance regression for request-response workloads Content-Language: en-US To: Eric Dumazet , Alexandra Winter Cc: David Miller , Jakub Kicinski , Yuchung Cheng , Soheil Hassas Yeganeh , Willem de Bruijn , Paolo Abeni , Mat Martineau , Saeed Mahameed , Niklas Schnelle , netdev , linux-s390@vger.kernel.org, Heiko Carstens References: <20220907122505.26953-1-wintera@linux.ibm.com> From: Christian Borntraeger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Mv-lsnKL3B6wBeXAACNoMkZhXubUdscA X-Proofpoint-GUID: GvcktbD9KF6_2vifa7qy07mGqh8-_705 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.528,FMLib:17.11.122.1 definitions=2022-09-08_06,2022-09-07_02,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 phishscore=0 priorityscore=1501 clxscore=1011 bulkscore=0 mlxlogscore=971 malwarescore=0 adultscore=0 suspectscore=0 spamscore=0 impostorscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2207270000 definitions=main-2209080034 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Am 07.09.22 um 18:06 schrieb Eric Dumazet: > On Wed, Sep 7, 2022 at 5:26 AM Alexandra Winter wrote: >> >> Since linear payload was removed even for single small messages, >> an additional page is required and we are measuring performance impact. >> >> 3613b3dbd1ad ("tcp: prepare skbs for better sack shifting") >> explicitely allowed "payload in skb->head for first skb put in the queue, >> to not impact RPC workloads." >> 472c2e07eef0 ("tcp: add one skb cache for tx") >> made that obsolete and removed it. >> When >> d8b81175e412 ("tcp: remove sk_{tr}x_skb_cache") >> reverted it, this piece was not reverted and not added back in. >> >> When running uperf with a request-response pattern with 1k payload >> and 250 connections parallel, we measure 13% difference in throughput >> for our PCI based network interfaces since 472c2e07eef0. >> (our IO MMU is sensitive to the number of mapped pages) > > > >> >> Could you please consider allowing linear payload for the first >> skb in queue again? A patch proposal is appended below. > > No. > > Please add a work around in your driver. > > You can increase throughput by 20% by premapping a coherent piece of > memory in which > you can copy small skbs (skb->head included) > > Something like 256 bytes per slot in the TX ring. > FWIW this regression was withthe standard mellanox driver (nothing s390 specific).