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[204.195.33.123]) by smtp.gmail.com with ESMTPSA id o1sm12157583pfh.191.2021.11.09.19.59.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Nov 2021 19:59:34 -0800 (PST) Date: Tue, 9 Nov 2021 19:59:31 -0800 From: Stephen Hemminger To: Narcisa Ana Maria Vasile Cc: Thomas Monjalon , dev@dpdk.org, dmitry.kozliuk@gmail.com, khot@microsoft.com, dmitrym@microsoft.com, roretzla@microsoft.com, talshn@nvidia.com, ocardona@microsoft.com, bruce.richardson@intel.com, david.marchand@redhat.com, pallavi.kadam@intel.com Message-ID: <20211109195931.2c26f51e@hermes.local> In-Reply-To: <20211110030417.GA7558@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> References: <1633732841-17873-1-git-send-email-navasile@linux.microsoft.com> <11591275.oo6G3FHbOz@thomas> <20211109015923.GB12569@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> <6965604.4qUlQkvJ3b@thomas> <20211110030417.GA7558@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [PATCH v16 2/9] eal: add thread attributes X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Tue, 9 Nov 2021 19:04:17 -0800 Narcisa Ana Maria Vasile wrote: > > > I'll send a new version with a better commit message. > > > Thread priorities on both Linux-based and Windows platforms are similarly > > > constructed from a class/policy + priority value. Currently in DPDK, most threads > > > operate at the OS-default priority level but there are cases when increasing the > > > priority is useful. For example, the Mellanox data path acceleration driver requires > > > realtime thread priority. Similarly, some Windows applications will require elevated > > > priority. > > > > It should not. We should not use realtime priority. > > Thomas, can you join the community sync tomorrow? I'll bring this up to discuss. > > High performance applications benefit from an option to raise the priority of their threads > to avoid being preemted by other threads on the system. If there are issues with realtime > priority on some of the platforms, maybe we can add a warning for the user to make them > aware of possible crashes as Stephen H. suggested some time ago. Note that this patch doesn't > change the priority of EAL threads, enabling the higher priority will be done through a command > line option when starting the application. > Maybe we can explore raising the priority but not to the realtime level. Let me put it more succulently. Almost all DPDK applications have threads that are a 100% CPU doing polling. Putting those thread as real-time thread breaks Linux badly because the kernel can and will try and run work on those CPU's and the system is broken/unstable/dead at that point. This is a case of different definitions and expectations of real-time in Linux and Windows. Linux definition of real-time priority is for well behaved and time critical applications. It expects RT applications to run, then sleep.