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([2620:10d:c090:500::6:6d67]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-314bc5cb670sm2895912eec.31.2026.07.24.13.08.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Jul 2026 13:08:03 -0700 (PDT) Message-ID: <01440106-92f0-4a4e-aef2-da2520820126@gmail.com> Date: Fri, 24 Jul 2026 13:08:03 -0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next V3] selftests: drv-net: Test queue stall upon reconfig To: Jakub Kicinski Cc: netdev@vger.kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, shuah@kernel.org, linux-kselftest@vger.kernel.org References: <20260723234857.2880270-1-mohsin.bashr@gmail.com> <20260724063744.7d0478da@kernel.org> Content-Language: en-US From: Mohsin Bashir In-Reply-To: <20260724063744.7d0478da@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/24/26 6:37 AM, Jakub Kicinski wrote: > On Thu, 23 Jul 2026 16:48:55 -0700 Mohsin Bashir wrote: >> Add a reconfig_tx_stall test that detects the possibility of a TX stall >> after ring reconfiguration. The key observation is that drivers using >> netif_tx_start_all_queues() are prone to experiencing a stall when >> reconfiguration completes compared to drivers using >> netif_tx_wake_all_queues(). start_all_queues only clears DRV_XOFF, while >> wake_all_queues also calls __netif_schedule() to kick the qdisc. Without >> the kick, qdisc backlog present at reconfig time can stay stuck until a >> new trigger is issued. > > AI CI says: > > The new `reconfig_tx_stall` test introduced by this patch is failing in > the NIPA CI on the netdevsim-based test environment (both regular and > debug kernels): > > not ok 3 ring_reconfig.reconfig_tx_stall > > Exception| File ".../ring_reconfig.py", line 331, in reconfig_tx_stall > Exception| raise KsftFailEx("failed to build qdisc backlog") > > The failure is a precondition failure — the test sends three bursts of > 128 SO_TXTIME packets at +100ms, +200ms, and +500ms delays and after each > burst checks whether a qdisc backlog has formed on the target TX queue. > No backlog appears after any of the three attempts. > > The test never reaches the actual ring-reconfig assertion; it fails > because the required qdisc backlog cannot be built on netdevsim under CI > conditions. This is likely because netdevsim drains its TX rings > (and/or releases SO_TXTIME packets) fast enough that no backlog > accumulates within the allotted windows, even with napi_defer_hard_irqs > set to 100 and the ring capped at 64 entries. > > The other two sub-tests (ring_reconfig.channels and > ring_reconfig.ringparam) continue to pass. > > Could you look into why the backlog-building phase does not work on > netdevsim? Possible approaches: > - Add a check/xfail if the backlog cannot be built after N attempts, > converting it from a hard failure to a xfail on virtual drivers > (prefer xfail over skip) Yeah, looks like netdevsim is not providing back-pressure on the TX path. I will change the fail to xfail in V4. > - Adjust the parameters (ring size, packet count, delay) so the > condition is more reliably triggered > - Mark the test as requiring a real NIC (nsim_test=False) if the > technique fundamentally doesn't work on virtual devices > and move it to the hw/ directory > > https://netdev-ctrl.bots.linux.dev/logview.html?f=/logs/vmksft/net-drv/results/747522/8-ring-reconfig-py/stdout