x86: Restore the critical section around whole ipi_bitmap_handler() if
hardclock IPI is delivered. In the current code after r355311, critical section is taken only around hardclockintr() call, and sched_preempt() is called after the section is exited. If we reschedule after exit, as we typically would due to conditions that caused IPI, in ULE the runq tdq_ipipending is not cleared, which blocks generation of further preempt IPIs. Since all relatively modern (10 years) hardware has per-cpu event timers, restoring the critical section conditionally does not affect it. Reported and tested by: cy Diagnosed and reviewed by: jeff (previous version) Sponsored by: The FreeBSD Foundation Differential revision: https://reviews.freebsd.org/D22716
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=355475
@ -1262,10 +1262,28 @@ ipi_bitmap_handler(struct trapframe frame)
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u_int ipi_bitmap;
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td = curthread;
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ipi_bitmap = atomic_readandclear_int(&cpuid_to_pcpu[cpu]->
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pc_ipi_bitmap);
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/*
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* sched_preempt() must be called to clear the pending preempt
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* IPI to enable delivery of further preempts. However, the
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* critical section will cause extra scheduler lock thrashing
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* when used unconditionally. Only critical_enter() if
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* hardclock must also run, which requires the section entry.
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*/
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if (ipi_bitmap & (1 << IPI_HARDCLOCK))
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critical_enter();
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td->td_intr_nesting_level++;
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oldframe = td->td_intr_frame;
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td->td_intr_frame = &frame;
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ipi_bitmap = atomic_readandclear_int(&cpuid_to_pcpu[cpu]->pc_ipi_bitmap);
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if (ipi_bitmap & (1 << IPI_PREEMPT)) {
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#ifdef COUNT_IPIS
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(*ipi_preempt_counts[cpu])++;
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#endif
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sched_preempt(td);
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}
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if (ipi_bitmap & (1 << IPI_AST)) {
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#ifdef COUNT_IPIS
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(*ipi_ast_counts[cpu])++;
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@ -1273,23 +1291,15 @@ ipi_bitmap_handler(struct trapframe frame)
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/* Nothing to do for AST */
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}
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if (ipi_bitmap & (1 << IPI_HARDCLOCK)) {
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critical_enter();
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#ifdef COUNT_IPIS
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(*ipi_hardclock_counts[cpu])++;
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#endif
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hardclockintr();
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critical_exit();
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}
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/* Run preempt after clock handlers since it may switch. */
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if (ipi_bitmap & (1 << IPI_PREEMPT)) {
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#ifdef COUNT_IPIS
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(*ipi_preempt_counts[cpu])++;
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#endif
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sched_preempt(td);
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}
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td->td_intr_frame = oldframe;
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td->td_intr_nesting_level--;
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if (ipi_bitmap & (1 << IPI_HARDCLOCK))
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critical_exit();
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}
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/*
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