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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> <2d71bab3-161d-414e-90e3-0e408ca931c2@linux.ibm.com> <20260224021924.GA53803@j66a10360.sqa.eu95> Content-Language: en-US From: Mahanta Jambigi In-Reply-To: <20260224021924.GA53803@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-Proofpoint-ORIG-GUID: pNvPn2sHG14hiX46wf5UKqYPx8oF_jQL X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI3MDAzNCBTYWx0ZWRfXx6WWfamxPlLg bNtFwvg5JIjHcD1Wu38YgDdHWeyGS48Vupc2wLhgofh7omoZ6CeQKqoiGrSymGpY1xwvTR92SMC sFQ4T5GpyiU7docCKuWafJ3rwFVRhRIBdh4TrSVCaHjJiglii+XPbJRnDSdVm5aqZuPNFkH0u5K orCBfEgLJdf4qF7gtemFRBPyRvKZ95FWQ0UPYY9ehzFUyjpiuvOFz1ekA4pktLu55ueSWUPfA09 UbUv/TKdPEkMyBT92Cu8prjB8GBXMTGnb5EhAPHBRdCC1STNbdjX2srOkRzoTwtRze9p6jls3QT TpWKXN3v95FtPK3VboFhKzKK0fHzqa5Lcz30U1SsS3P+bflx34UlWplFkzQuA+dxqr7q5gtYIQK gmbrWDOVrCof75RRfF7rlAjRs5Sf3y/a706FFB448Uk9F8AdIP9V8MqlpUGHUh1Pd9xh/9j0+tq Mw12Nh8V38q729Ielng== X-Authority-Analysis: v=2.4 cv=eNceTXp1 c=1 sm=1 tr=0 ts=69a1208b 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=KFbtujwD9d188Aqvv-QA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: ob1o3a-7dAjm5dkH_lGYA3DimTJbH9ZQ 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=2026-02-27_01,2026-02-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 priorityscore=1501 phishscore=0 suspectscore=0 adultscore=0 bulkscore=0 lowpriorityscore=0 malwarescore=0 impostorscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602270034 On 24/02/26 7:49 am, D. Wythe wrote: > On Fri, Feb 13, 2026 at 04:53:28PM +0530, Mahanta Jambigi wrote: >> >> >> 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 >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > > Using the exact same XML profile you provided, I tested this on a 25Gb > NIC. I observed no degradation. Instead, performance improved > significantly: > > Original: ~1.08 Gb/s > Patched: ~5.1 Gb/s > > I suspect the 59% drop might be due to connections falling back to TCP. > Could you check smcss -a during your test to see if the traffic is > actually running over SMC-R? I have checked this. The connection was successful using *SMCR* Mode itself. Also I have confirmed this via 'smcr -d stats' command which shows 0 count for TCP fallback. > >> >> 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 > > Here are the exact commands and scripts I used for the > redis-benchmark: > > Server: smc_run redis-server --protected-mode no --save > > Client: smc_run redis-benchmark -h -n 5000000 -t set --threads 3 > -c > > D. Wythe