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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: CO1PR21MB1297.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: b7498b3b-380f-41b1-c47b-08d9a46a85e7 X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Nov 2021 16:52:46.8349 (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: QrEO0SE5c1seBafYPeWuQvBDYYwhcocFnXCplz6yxpkARSiDucI9GIE1C67YHn9vntjDTcsbBDSdIFODsTIM2Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR21MB2025 X-Mailman-Approved-At: Thu, 11 Nov 2021 01:02:08 +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: Bruce Richardson =20 Sent: Wednesday, November 10, 2021 1:21 AM To: Stephen Hemminger Cc: Tyler Retzlaff ; Narcisa Ana Maria Vasile ; thomas ; dev@dpdk.org; Dmit= ry Kozlyuk ; Khoa To ; Dmitry= Malloy ; talshn ; Omar Cardona= ; david.marchand@redhat.com; Kadam, Pallavi Subject: Re: [EXTERNAL] Re: [dpdk-dev] [PATCH v16 2/9] eal: add thread attr= ibutes > On Tue, Nov 09, 2021 at 10:29:25PM -0800, Stephen Hemminger wrote: > > On Wed, 10 Nov 2021 04:20:52 +0000 > > Tyler Retzlaff wrote: > >=20 > > > > > > > > > > High performance applications benefit from an option to raise=20 > > > > > the priority of their threads to avoid being preemted by other=20 > > > > > threads on the system. If there are issues with realtime=20 > > > > > priority on some of the platforms, maybe we can add a warning=20 > > > > > for the user to make them aware of possible crashes as Stephen=20 > > > > > H. suggested some time ago. Note that this patch doesn't change t= he priority of EAL threads, enabling the higher priority will be done throu= gh a command line option when starting the application. > > > > > Maybe we can explore raising the priority but not to the realtime= level. =20 > > >=20 > > > > 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. =20 > > >=20 > > > The suggestion is that when running on Windows it should be possible = for the application to be configured to use real-time threads, there is no = implication that it will force real-time priority on Linux. If it doesn't = make sense for it to be configured on Linux then don't configure it. But s= aying it shall not be configurable for any platform just because one platfo= rm can't make use of the configuration and those platforms have to run comp= romised makes little sense. Linux administrators are (or should be) knowle= dgeable enough to know what configuration to use. > > > > >=20 > > Why not just make it always return an error when real-time is requested= on Linux from a DPDK thread. > > > I would tend to agree with this suggestion, that we just return ENOTSUP e= rror code for Linux. It's too easy to lock up a linux system with realtime = DPDK threads. If a user really knows what they are doing and they need real= time priority on linux, they can use the linux scheduler APIs directly. This sounds reasonable to me. It doesn't compromise the Linux platform and= allows the Windows platform to reach potential. > However, I am ok with having such a function supported on Windows if it's= needed. Unfortunately, I don't know for sure about BSD, but it probably sh= ould follow the linux approach initially unless proved safe. Agreed, probably true for all POSIX platforms that support RT extensions.