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Tue, 15 Sep 2020 05:25:27 +0000 Subject: Re: [PATCH bpf-next] bpf: using rcu_read_lock for bpf_sk_storage_map iterator To: Song Liu CC: bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , Martin KaFai Lau References: <20200914184630.1048718-1-yhs@fb.com> From: Yonghong Song Message-ID: <86ee274b-a23c-25aa-6ec3-e1448667b6b4@fb.com> Date: Mon, 14 Sep 2020 22:25:23 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MWHPR22CA0063.namprd22.prod.outlook.com (2603:10b6:300:12a::25) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21cf::19e4] (2620:10d:c090:400::5:ae1) by MWHPR22CA0063.namprd22.prod.outlook.com (2603:10b6:300:12a::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3370.16 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 227b14e3-1b3b-43bb-7ea2-08d85937c0c1 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Sep 2020 05:25:27.2780 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 5t/qpkWvyDstXFn7d/pOVEb60pHjhMvdpAKdapayHoap/f42VZ1/QK5gTDkKZErx X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2775 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-15_04:2020-09-15,2020-09-15 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 clxscore=1015 malwarescore=0 lowpriorityscore=0 suspectscore=0 mlxscore=0 mlxlogscore=999 bulkscore=0 priorityscore=1501 phishscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150051 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 9/14/20 2:28 PM, Song Liu wrote: > On Mon, Sep 14, 2020 at 11:47 AM Yonghong Song wrote: >> >> Currently, we use bucket_lock when traversing bpf_sk_storage_map >> elements. Since bpf_iter programs cannot use bpf_sk_storage_get() >> and bpf_sk_storage_delete() helpers which may also grab bucket lock, >> we do not have a deadlock issue which exists for hashmap when >> using bucket_lock ([1]). > > The paragraph above describes why we can use bucket_lock, which is more > or less irrelevant to this change. Also, I am not sure why we refer to [1] here. What I try to clarify here is unlike [1], we do not have bugs with the current code. But I guess no bugs is implicit so I probably do not need to say anything. Will skip the above paragraph in the next revision. > >> >> If a bucket contains a lot of sockets, during bpf_iter traversing >> a bucket, concurrent bpf_sk_storage_{get,delete}() may experience >> some undesirable delays. Using rcu_read_lock() is a reasonable > > It will be great to include some performance comparison. Sure. Let me give some try to collect some statistics. > >> compromise here. Although it may lose some precision, e.g., >> access stale sockets, but it will not hurt performance of other >> bpf programs. >> >> [1] https://lore.kernel.org/bpf/20200902235341.2001534-1-yhs@fb.com >> >> Cc: Martin KaFai Lau >> Signed-off-by: Yonghong Song > > Other than these, > > Acked-by: Song Liu > > [...] >