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The hrtimer interrupt expires timers and at the end of the interrupt it rearms the clockevent device for the next expiring timer. That's obviously correct, but in the case that a expired timer set NEED_RESCHED the return from interrupt ends up in schedule(). If HRTICK is enabled then schedule() will modify the hrtick timer, which causes another reprogramming of the hardware. That can be avoided by deferring the rearming to the return from interrupt path and if the return results in a immediate schedule() invocation then it can be deferred until the end of schedule(). To make this correct the affected code parts need to be made aware of this. Provide empty stubs for the deferred rearming mechanism, so that the relevant code changes for entry, softirq and scheduler can be split up into separate changes independent of the actual enablement in the hrtimer code. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/20260224163431.000891171@kernel.org