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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SJ0PR21MB1312.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2538fe6c-6cfc-4c63-a27c-08d9a4017c0a X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Nov 2021 04:20:52.9882 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: h0gKFAu5hOkbGLfFc4e0Y6zpTiyIQ3JoU4mToQkouC8UDcEFf/PqLXLX8CYui6gJV088hb9gyQEnF9fBp48WfQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR21MB1887 X-Mailman-Approved-At: Wed, 10 Nov 2021 15:00:26 +0100 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 -----Original Message----- From: Stephen Hemminger =20 Sent: Tuesday, November 9, 2021 8:00 PM To: Narcisa Ana Maria Vasile Cc: thomas ; dev@dpdk.org; Dmitry Kozlyuk ; Khoa To ; Dmitry Malloy ; Tyler Retzlaff ; talshn ; Omar Cardona ; bruce.richardson@intel.com; da= vid.marchand@redhat.com; Kadam, Pallavi Subject: [EXTERNAL] Re: [dpdk-dev] [PATCH v16 2/9] eal: add thread attribut= es 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 s= imilarly > > > > constructed from a class/policy + priority value. Currently in DP= DK, 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 accelerat= ion driver requires > > > > realtime thread priority. Similarly, some Windows applications wi= ll require elevated > > > > priority. =20 > > >=20 > > > It should not. We should not use realtime priority. =20 > > > > 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=20 > > priority of their threads to avoid being preemted by other threads on=20 > > the system. If there are issues with realtime priority on some of the=20 > > platforms, maybe we can add a warning for the user to make them aware=20 > > of possible crashes as Stephen H. suggested some time ago. Note that=20 > > this patch doesn't change the priority of EAL threads, enabling the hig= her priority will be done through a command line option when starting the a= pplication. > > 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 polli= ng. > Putting those thread as real-time thread breaks Linux badly because the k= ernel can and will try and run work on those CPU's and the system is broken= /unstable/dead at that point. The suggestion is that when running on Windows it should be possible for th= e application to be configured to use real-time threads, there is no implic= ation that it will force real-time priority on Linux. If it doesn't make s= ense for it to be configured on Linux then don't configure it. But saying = it shall not be configurable for any platform just because one platform can= 't make use of the configuration and those platforms have to run compromise= d makes little sense. Linux administrators are (or should be) knowledgeabl= e enough to know what configuration to use. > > This is a case of different definitions and expectations of real-time i= n Linux and Windows. Linux definition of real-time priority is for well be= haved and time critical applications. It expects RT applications to run, th= en sleep.