** Changed in: intel Status: Fix Committed => Fix Released -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1084377
Title: [Feature] non-lazy extended state restore during process context switch Status in intel: Fix Released Status in “linux” package in Ubuntu: Fix Released Status in “linux” source package in Raring: Fix Released Bug description: Fundamental model of the current Linux kernel is to lazily restore extended-state (xstate like FP/SSE/AVX) during context switch. On the first use of the xstate after context-switch, application takes a #DNA exception and the kernel will restore it. After 5 such consecutive xstate usages post task-switch, kernel adopts a heuristic to pre-load the xstate during context-switch for the next 251 task-switches. This feature changes that fundamental lazy model to the non-lazy model for the processors supporting any new xstate feature beyond AVX (In essence making the pre-load heuristic as the fundamental model). While this is a must for enabling some of the new features in the next generation processor after Broadwell, as we saw some performance improvements (like avoiding unnecessary DNA exceptions, improving the kernel code that uses fpu inside the kernel etc), we enabled this behavior for all cpu's supporting xsaveopt. So it will be from SNB. Upstream status: Code in 3.7-rc1: 050902c011712ad4703038fa4489ec4edd87d396 0ca5bd0d886578ad0afeceaa83458c0f35cb3c6b 72a671ced66db6d1c2bfff1c930a101ac8d08204 e962591749dfd4df9fea2c530ed7a3cfed50e5aa 377ffbcc536a5a6666dc077395163ab149c02610 9c1c3fac53378c9782c18f80107965578d7b7167 841e3604d35aa70d399146abdc526d8c89a2c2f5 9c6ff8bbb69a4e7b47ac40bfa44509296e89c5c0 304bceda6a18ae0b0240b8aac9a6bdf8ce2d2469 5d2bd7009f306c82afddd1ca4d9763ad8473c216 212b02125f3725127148475059a70031bd031bdb e00229819f306b1f86134095347e9187dc346bd1 a8615af4bc3621cb01096541dafa6f68352ec2d9 Some data on a two socket SNB system: * Saved 20K DNA exceptions during boot on a two socket SNB system. * Saved 50K DNA exceptions during kernel-compilation workload. * Improved throughput of the AVX based checksumming function inside the kernel by ~15% as xsave/xrstor is faster than the serializing clts/stts pair. DNA stands for (Device Not Available). To manage notifications about this bug go to: https://bugs.launchpad.net/intel/+bug/1084377/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp