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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2dd608d1939sm1831637a91.33.2024.09.18.09.06.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Sep 2024 09:06:12 -0700 (PDT) Date: Wed, 18 Sep 2024 09:06:10 -0700 From: Stephen Hemminger <stephen@networkplumber.org> To: Wojciech Panfil <wojciech.panfil@intel.com> Cc: <bruce.richardson@intel.com>, <pallavi.kadam@intel.com>, <dev@dpdk.org>, <jacek.kalwas@intel.com>, <konrad.sztyber@intel.com>, <dmitry.kozliuk@gmail.com>, <roretzla@linux.microsoft.com> Subject: Re: [PATCH] eal/alarm_cancel: Fix thread starvation Message-ID: <20240918090610.1dcfb37c@hermes.local> In-Reply-To: <20240918113906.64350-1-wojciech.panfil@intel.com> References: <20240918113906.64350-1-wojciech.panfil@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions <dev.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/dev>, <mailto:dev-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/dev/> List-Post: <mailto:dev@dpdk.org> List-Help: <mailto:dev-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/dev>, <mailto:dev-request@dpdk.org?subject=subscribe> Errors-To: dev-bounces@dpdk.org On Wed, 18 Sep 2024 13:39:06 +0200 Wojciech Panfil <wojciech.panfil@intel.com> wrote: > Issue: > Two threads: > > - A, executing rte_eal_alarm_cancel, > - B, executing eal_alarm_callback. > > Such case can cause starvation of thread B. Please see that there is a > small time window between lock and unlock in thread A, so thread B must > be switched to within a very small time window, so that it can obtain > the lock. > > Solution to this problem is use sched_yield(), which puts current thread > (A) at the end of thread execution priority queue and allows thread B to > execute. > > The issue can be observed e.g. on hot-pluggable device detach path. > On such path, rte_alarm can used to check if DPDK has completed > the detachment. Waiting for completion, rte_eal_alarm_cancel > is called, while another thread periodically calls eal_alarm_callback > causing the issue to occur. > > Signed-off-by: Wojciech Panfil <wojciech.panfil@intel.com> Make sense. Alarm is non-EAL thread, and so is hotplug. Acked-by: Stephen Hemminger <stephen@networkplumber.org> Does the timer_stop code have similar issues? Probably only if users do unexpected things like map multiple logical lcores to same CPU.