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posix CPU timers into task work context. The tick interrupt is reduced to a quick check which queues the work which is doing the heavy lifting before returning to user space or going back to guest mode. Moving this out is deferring the signal delivery slightly but posix CPU timers are inaccurate by nature as they depend on the tick so there is no real damage. The relevant test cases all passed. This lifts the last offender for RT out of the hard interrupt context tick handler, but it also has the general benefit that the actual heavy work is accounted to the task/process and not to the tick interrupt itself. Further optimizations are possible to break long sighand lock hold and interrupt disabled (on !RT kernels) times when a massive amount of posix CPU timers (which are unpriviledged) is armed for a task/process. This is currently only enabled for x86 because the architecture has to ensure that task work is handled in KVM before entering a guest, which was just established for x86 with the new common entry/exit code which got merged post 5.8 and is not the case for other KVM architectures. -----BEGIN PGP SIGNATURE----- iQJHBAABCgAxFiEEQp8+kY+LLUocC4bMphj1TA10mKEFAl82sRkTHHRnbHhAbGlu dXRyb25peC5kZQAKCRCmGPVMDXSYoUs2D/9IZuALnVXtnvsOQh5uMRpxr/I6tpQm KJSRkcSSne9rIV3dQlswDdaT7bGibd7pbKQOnlA0vc37vDwaJHEzmTOJGpHpHnMA fHH2QP3LL2oZ1d7DG6eNJESCmaFBcaYXNbKtluOWQzHQhd9P8yHb4N+kzfxHK0Fr uNd+cd6T658xPsNOLaLP3MG2Yz0rVt2F5c1v8n78NfibeKckYhPov8cwVrf2WGWr XFHKorx4lXZ+vFwKEeZ7qQtqvAsLDixgMkFfY2GGSPhd1AMAaIUICZgsdEj2gg7H YK+lwA0uoqPaXshOCmdkCLkfPA7BRmAySWE7jUPbIvRqM94Uapk9+4CqjgiH1Qs+ T8CWbcZk8tZACFrouhZkhrnjUTev/vE7oirsjn26DRY68/Ec7llpCOjvVA7HZWqN vJ/BN35IufA7WEkf2TWNv5mg1zIlHI0O17zDifFq4g2VKFDVvQB0QYWlvug/eAu9 zYNX3WwA/IP8C9EOHZt54e6AKH8F3dT04oLFUkmRIcVKv1SEbdFufVfV7RavPEwK P21JNXPDdd0aLUO7ksqyQN7pyR3puGXSCb5NAPtZY6UWSMN4G/3SVry3mJa/0BJd mn+uYGpo9vmceh90vAHBoGIena/pez/PyRLWgGeT9jMjk95rNY0sEhaLEAOF9AR5 ck+3K2rY0S3wwQ== =Reot -----END PGP SIGNATURE----- Merge tag 'timers-core-2020-08-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull more timer updates from Thomas Gleixner: "A set of posix CPU timer changes which allows to defer the heavy work of posix CPU timers into task work context. The tick interrupt is reduced to a quick check which queues the work which is doing the heavy lifting before returning to user space or going back to guest mode. Moving this out is deferring the signal delivery slightly but posix CPU timers are inaccurate by nature as they depend on the tick so there is no real damage. The relevant test cases all passed. This lifts the last offender for RT out of the hard interrupt context tick handler, but it also has the general benefit that the actual heavy work is accounted to the task/process and not to the tick interrupt itself. Further optimizations are possible to break long sighand lock hold and interrupt disabled (on !RT kernels) times when a massive amount of posix CPU timers (which are unpriviledged) is armed for a task/process. This is currently only enabled for x86 because the architecture has to ensure that task work is handled in KVM before entering a guest, which was just established for x86 with the new common entry/exit code which got merged post 5.8 and is not the case for other KVM architectures" * tag 'timers-core-2020-08-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86: Select POSIX_CPU_TIMERS_TASK_WORK posix-cpu-timers: Provide mechanisms to defer timer handling to task_work posix-cpu-timers: Split run_posix_cpu_timers() |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.