From: "Dmitry Malloy (MESHCHANINOV)" <email@example.com> To: Stephen Hemminger <firstname.lastname@example.org>, Tal Shnaiderman <email@example.com> Cc: Dmitry Kozlyuk <firstname.lastname@example.org>, Narcisa Ana Maria Vasile <Narcisa.Vasile@microsoft.com>, Eilon Greenstein <email@example.com>, Omar Cardona <firstname.lastname@example.org>, Rani Sharoni <email@example.com>, Odi Assli <firstname.lastname@example.org>, Harini Ramakrishnan <Harini.Ramakrishnan@microsoft.com>, thomas <email@example.com>, "firstname.lastname@example.org" <email@example.com> Subject: Re: [dpdk-dev] [EXTERNAL] Re: Windows DPDK real-time priority threads causing thread starvation Date: Wed, 9 Dec 2020 16:12:10 +0000 Message-ID: <DM5PR21MB18167C9CA7B39F83D9C6A016B3CC1@DM5PR21MB1816.namprd21.prod.outlook.com> (raw) In-Reply-To: <firstname.lastname@example.org> There is a configuration in Windows similar to Linux isolcpus where scheduler tries not to run anything on such cores, and implementation is being enhanced for the next Windows release with User-mode vmswitch feedback. I'll dig out the details. Dmitry -----Original Message----- From: Stephen Hemminger <email@example.com> Sent: Wednesday, December 9, 2020 8:09 AM To: Tal Shnaiderman <firstname.lastname@example.org> Cc: Dmitry Kozlyuk <email@example.com>; Dmitry Malloy (MESHCHANINOV) <firstname.lastname@example.org>; Narcisa Ana Maria Vasile <Narcisa.Vasile@microsoft.com>; Eilon Greenstein <email@example.com>; Omar Cardona <firstname.lastname@example.org>; Rani Sharoni <email@example.com>; Odi Assli <firstname.lastname@example.org>; Harini Ramakrishnan <Harini.Ramakrishnan@microsoft.com>; thomas <email@example.com>; firstname.lastname@example.org Subject: [EXTERNAL] Re: [dpdk-dev] Windows DPDK real-time priority threads causing thread starvation On Wed, 9 Dec 2020 14:15:30 +0000 Tal Shnaiderman <email@example.com> wrote: > Hi, > > During our verification tests on Windows DPDK we've noticed that DPDK polling threads, which run in REALTIME_PRIORITY_CLASS are causing starvation to other threads from the OS which need to change affinity and run in lower priority. > > While running an application for a while we see the OS thread waits for 2:30 minutes and raises a bugcheck, see below example of such flow: > > 1) DPDK thread running on core-0 in real-time high priority(24) polling mode. > 2) The thread is blocking the system function NtSetSystemInformation > (ExpUpdateTimerConfiguration) in another thread from > switching to core-0 via KeSetSystemGroupAffinityThread since the > calling thread is priority 15. > 3) NtSetSystemInformation exclusively acquired system-wide lock > (ExpTimeRefreshLock) hence > it blocks other threads (e.g. calling NtQuerySystemInformation). > > We've seen this behavior only while running on Windows 2019 VMs, maybe on native machines OS scheduling of such flow is done differently? > > Below is usage explanation from the documentation of SetPriorityClass : > > - REALTIME_PRIORITY_CLASS > Process that has the highest possible priority. The threads of the process preempt the threads of all other processes, including operating system processes performing important tasks. For example, a real-time process that executes for more than a very brief interval can cause disk caches not to flush or cause the mouse to be unresponsive. > > So I assume using this kind of thread for a long period as we do can cause unstable behavior. > > How do you think we can resolve this? Are there such cases in Linux? > >  - > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs > .microsoft.com%2Fen-us%2Fwindows%2Fwin32%2Fapi%2Fprocessthreadsapi%2Fn > f-processthreadsapi-setpriorityclass&data=04%7C01%7Cdmitrym%40micr > osoft.com%7C623844c12bc2440d3bbd08d89c5cc0f1%7C72f988bf86f141af91ab2d7 > cd011db47%7C1%7C0%7C637431269479649074%7CUnknown%7CTWFpbGZsb3d8eyJWIjo > iMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000& > ;sdata=LSv%2F%2BZMxUkfgcQVD778wL4JbVdl2qYV1tHdfVrEck4c%3D&reserved > =0 > > Thanks, > > Tal. This is not unique to Windows, Linux has same thing when using SCHED_FIFO. Setting REALTIME is not a magic "go fast" flag it tells scheduler to "run this thread at higher priority than kernel". Setting real time is not compatible with applications doing 100% polling. If you have to use REALTIME then application must change to doing sleep/wakeup type architecture, not pure polling. Typical DPDK style application is incompatible with SCHED_FIFO/SCHED_RR.
next prev parent reply other threads:[~2020-12-10 16:21 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-09 14:15 [dpdk-dev] " Tal Shnaiderman 2020-12-09 16:08 ` John Alexander 2020-12-09 16:08 ` Stephen Hemminger 2020-12-09 16:12 ` Dmitry Malloy (MESHCHANINOV) [this message] 2020-12-16 14:53 ` [dpdk-dev] [EXTERNAL] " Tal Shnaiderman
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