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Commit85e511df3c("sched/eevdf: Allow shorter slices to wakeup-preempt") introduced a mechanism that a wakee with shorter slice could preempt the current running task. It also lower the bar for the current task to be preempted, by checking the rq->nr_running instead of cfs_rq->nr_running when the current task has ran out of time slice. But there is a scenario that is problematic. Say, if there is 1 cfs task and 1 rt task, before85e511df3c, update_deadline() will not trigger a reschedule, and after85e511df3c, since rq->nr_running is 2 and resched is true, a resched_curr() would happen. Some workloads (like the hackbench reported by lkp) do not like over-scheduling. We can see that the preemption rate has been increased by 2.2%: 1.654e+08 +2.2% 1.69e+08 hackbench.time.involuntary_context_switches Restore its previous check criterion. Fixes:85e511df3c("sched/eevdf: Allow shorter slices to wakeup-preempt") Closes: https://lore.kernel.org/oe-lkp/202409231416.9403c2e9-oliver.sang@intel.com Reported-by: kernel test robot <oliver.sang@intel.com> Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com> Signed-off-by: Chen Yu <yu.c.chen@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Honglei Wang <jameshongleiwang@126.com> Tested-by: K Prateek Nayak <kprateek.nayak@amd.com> Link: https://lore.kernel.org/r/20240925085440.358138-1-yu.c.chen@intel.com
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 reStructuredText 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.