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Wythe" Cc: "David S. Miller" , Dust Li , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Sidraya Jayagond , Wenjia Zhang , Simon Horman , Tony Lu , Wen Gu , linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, netdev@vger.kernel.org, oliver.yang@linux.alibaba.com, pasic@linux.ibm.com References: <20260202094800.30373-1-alibuda@linux.alibaba.com> <20260209075338.GA61095@j66a10360.sqa.eu95> Content-Language: en-US From: Mahanta Jambigi In-Reply-To: <20260209075338.GA61095@j66a10360.sqa.eu95> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=YZiwJgRf c=1 sm=1 tr=0 ts=698f09c0 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=sCxrbXXTP0iVI5IyWHIA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: YMBInZTsF0iReiqleGmzV9rtjq0lA3Ln X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjEzMDA4NyBTYWx0ZWRfX2ZXZvS03WpgZ xjlA6FSncLY4fquK3+Tx/ApJ/pwHcVYkjn4ZrbrQGzmHbC486ssaf5jIR3yD/K2T5+maZOjnGze AXcxe983doBoUm1CE9lJQs/bqe+eRHBa6QLhsMz93ZAMBciKydSMUcEIPMVRFs+u9y754CREel4 zgO3/Ow501J4nMDUdYx4jn2w8XvY2CkmwGDB8inTRQd7bWx9/L3lFIi3vWLTWqG3bZ/y4nr75V6 5aWcmk8QygTu6sKuUrVdV5BrQhNYbtTW1LZA7uEA+oy+Dg4iSS6Fkc0F2C6sS0lD547F0P1Y95A vfDfNF3Ns8y3FyoGp2z8xOoqCJCB9Gbk2rqbtgBnoFmdtO6ak/l8Y3GQiAg6jIStDFwSf0NC/Dq V+POv7vqUbxJCd/x0DfwSscyimZNTvKjTDVkQi8C3P0ch8EjJ5IrPhQZ6k8PZnFi4sECP65baeQ 6XQAx8hv59H4J4yXGtA== X-Proofpoint-GUID: fH95bB4F1c2GTD7iNl3j9nufPkURUWjM X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-13_02,2026-02-12_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 impostorscore=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 adultscore=0 clxscore=1015 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602130087 On 09/02/26 1:23 pm, D. Wythe wrote: > On Fri, Feb 06, 2026 at 04:58:23PM +0530, Mahanta Jambigi wrote: >> >> >> On 02/02/26 3:18 pm, D. Wythe wrote: >>> The current SMC-R implementation relies on global per-device CQs >>> and manual polling within tasklets, which introduces severe >>> scalability bottlenecks due to global lock contention and tasklet >>> scheduling overhead, resulting in poor performance as concurrency >>> increases. >>> >>> Refactor the completion handling to utilize the ib_cqe API and >>> standard RDMA core CQ pooling. This transition provides several key >>> advantages: >>> >>> 1. Multi-CQ: Shift from a single shared per-device CQ to multiple >>> link-specific CQs via the CQ pool. This allows completion processing >>> to be parallelized across multiple CPU cores, effectively eliminating >>> the global CQ bottleneck. >>> >>> 2. Leverage DIM: Utilizing the standard CQ pool with IB_POLL_SOFTIRQ >>> enables Dynamic Interrupt Moderation from the RDMA core, optimizing >>> interrupt frequency and reducing CPU load under high pressure. >>> >>> 3. O(1) Context Retrieval: Replaces the expensive wr_id based lookup >>> logic (e.g., smc_wr_tx_find_pending_index) with direct context retrieval >>> using container_of() on the embedded ib_cqe. >>> >>> 4. Code Simplification: This refactoring results in a reduction of >>> ~150 lines of code. It removes redundant sequence tracking, complex lookup >>> helpers, and manual CQ management, significantly improving maintainability. >>> >>> Performance Test: redis-benchmark with max 32 connections per QP >>> Data format: Requests Per Second (RPS), Percentage in brackets >>> represents the gain/loss compared to TCP. >>> >>> | Clients | TCP | SMC (original) | SMC (cq_pool) | >>> |---------|----------|---------------------|---------------------| >>> | c = 1 | 24449 | 31172 (+27%) | 34039 (+39%) | >>> | c = 2 | 46420 | 53216 (+14%) | 64391 (+38%) | >>> | c = 16 | 159673 | 83668 (-48%) <-- | 216947 (+36%) | >>> | c = 32 | 164956 | 97631 (-41%) <-- | 249376 (+51%) | >>> | c = 64 | 166322 | 118192 (-29%) <-- | 249488 (+50%) | >>> | c = 128 | 167700 | 121497 (-27%) <-- | 249480 (+48%) | >>> | c = 256 | 175021 | 146109 (-16%) <-- | 240384 (+37%) | >>> | c = 512 | 168987 | 101479 (-40%) <-- | 226634 (+34%) | >>> >>> The results demonstrate that this optimization effectively resolves the >>> scalability bottleneck, with RPS increasing by over 110% at c=64 >>> compared to the original implementation. >> >> I applied your patch to the latest kernel(6.19-rc8) & saw below >> Performance results: >> >> 1) In my evaluation, I ran several *uperf* based workloads using a >> request/response (RR) pattern, and I observed performance *degradation* >> ranging from *4%* to *59%*, depending on the specific read/write sizes >> used. For example, with a TCP RR workload using 50 parallel clients >> (nprocs=50) sending a 200‑byte request and reading a 1000‑byte response >> over a 60‑second run, I measured approximately 59% degradation compared >> to SMC‑R original performance. >> > > The only setting I changed was net.smc.smcr_max_conns_per_lgr = 32, all > other parameters were left at their default values. redis-benchmark is a > classic Request/Response (RR) workload, which contradicts your test > results. Since I'm unable to reproduce your results, it would be > very helpful if you could share the specific test configuration for my > analysis. I used a simple client–server setup connected via 25 Gb/s RoCE_Express2 adapters on the same LAN(connection established via SMC-R v1). After running the commands shown below, I observed a performance degradation of up to 59%. Server: smc_run uperf -s Client: smc_run uperf -m rr1c-200x1000-50.xml cat rr1c-200x1000-50.xml I installed redis-server on the server machine & redis-benchmark on the client machine & I was able to establish the SMC-R using below commands. If you could help me with the exact commands you used to measure the redis-benchmark performance, I can try the same on my setup. Server: smc_run redis-server --port --save "" --appendonly no --protected-mode no --bind 0.0.0.0 Client: smc_run redis-benchmark -h -p -n 10000 -c 50 -t ping_inline,ping_bulk -q