Date: Sat, 20 Oct 2012 12:07:49 +0000 (UTC) From: Marius Strobl <marius@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r241780 - in head/sys/sparc64: include sparc64 Message-ID: <201210201207.q9KC7nWF023822@svn.freebsd.org>
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Author: marius Date: Sat Oct 20 12:07:48 2012 New Revision: 241780 URL: http://svn.freebsd.org/changeset/base/241780 Log: - Give PIL_PREEMPT the lowest priority just above low/stray interrupts. The reason for this is that the SPARC v9 architecture allows nested interrupts of higher priority/level than that of the current interrupt to occur (and we can't just entirely bypass this model, also, at least for tick interrupts, this also wouldn't be wise). However, when a preemption interrupt interrupts another interrupt of lower priority, f.e. PIL_ITHREAD, and that one in turn is nested by a third interrupt, f.e. PIL_TICK, with SCHED_ULE the execution of interrupts higher than PIL_PREEMPT may be migrated to another CPU. In particular, tl1_ret(), which is responsible for restoring the state of the CPU prior to entry to the interrupt based on the (also migrated) trap frame, then is run on a CPU which actually didn't receive the interrupt in question, causing an inappropriate processor interrupt level to be "restored". In turn, this causes interrupts of the first level, i.e. PIL_ITHREAD in the above scenario, to be blocked on the target of the migration until the correct PIL happens to be restored again on that CPU again. Making PIL_PREEMPT the lowest real priority, this effectively prevents this scenario from happening, as preemption interrupts no longer can interrupt any other interrupt besides stray ones (which is no issue). Thanks to attilio@ and especially mav@ for helping me to understand this problem at the 201208DevSummit. - Give PIL_STOP (which is also used for IPI_STOP_HARD, given that there's no real equivalent to NMIs on SPARC v9) the highest possible priority just below the hardwired PIL_TICK, so it has a chance to interrupt more things. MFC after: 1 week Modified: head/sys/sparc64/include/intr_machdep.h head/sys/sparc64/sparc64/intr_machdep.c Modified: head/sys/sparc64/include/intr_machdep.h ============================================================================== --- head/sys/sparc64/include/intr_machdep.h Sat Oct 20 10:51:32 2012 (r241779) +++ head/sys/sparc64/include/intr_machdep.h Sat Oct 20 12:07:48 2012 (r241780) @@ -41,14 +41,14 @@ #define IV_SHIFT 6 #define PIL_LOW 1 /* stray interrupts */ -#define PIL_ITHREAD 2 /* interrupts that use ithreads */ -#define PIL_RENDEZVOUS 3 /* smp rendezvous ipi */ -#define PIL_AST 4 /* ast ipi */ -#define PIL_STOP 5 /* stop cpu ipi */ -#define PIL_PREEMPT 6 /* preempt idle thread cpu ipi */ -#define PIL_HARDCLOCK 7 /* hardclock broadcast */ -#define PIL_FILTER 12 /* filter interrupts */ -#define PIL_BRIDGE 13 /* bridge interrupts */ +#define PIL_PREEMPT 2 /* preempt idle thread CPU IPI */ +#define PIL_ITHREAD 3 /* interrupts that use ithreads */ +#define PIL_RENDEZVOUS 4 /* SMP rendezvous IPI */ +#define PIL_AST 5 /* asynchronous trap IPI */ +#define PIL_HARDCLOCK 6 /* hardclock broadcast */ +#define PIL_FILTER 11 /* filter interrupts */ +#define PIL_BRIDGE 12 /* bridge interrupts */ +#define PIL_STOP 13 /* stop CPU IPI */ #define PIL_TICK 14 /* tick interrupts */ #ifndef LOCORE Modified: head/sys/sparc64/sparc64/intr_machdep.c ============================================================================== --- head/sys/sparc64/sparc64/intr_machdep.c Sat Oct 20 10:51:32 2012 (r241779) +++ head/sys/sparc64/sparc64/intr_machdep.c Sat Oct 20 12:07:48 2012 (r241780) @@ -92,15 +92,15 @@ static uint16_t intr_stray_count[IV_MAX] static const char *const pil_names[] = { "stray", "low", /* PIL_LOW */ + "preempt", /* PIL_PREEMPT */ "ithrd", /* PIL_ITHREAD */ "rndzvs", /* PIL_RENDEZVOUS */ "ast", /* PIL_AST */ - "stop", /* PIL_STOP */ - "preempt", /* PIL_PREEMPT */ "hardclock", /* PIL_HARDCLOCK */ "stray", "stray", "stray", "stray", "filter", /* PIL_FILTER */ "bridge", /* PIL_BRIDGE */ + "stop", /* PIL_STOP */ "tick", /* PIL_TICK */ };
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