Messages in this thread | | | Date | Mon, 12 Jun 2006 20:37:43 +0200 | From | Andreas Mohr <> | Subject | [RFC -mm] more cpu_relax() places? |
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Hi all,
while reviewing 2.6.17-rc6-mm1, I found some places that might want to make use of cpu_relax() in order to not block secondary pipelines while busy-polling (probably especially useful on SMT CPUs):
arch/i386/kernel/smp.c/flush_tlb_others():
while (!cpus_empty(flush_cpumask)) /* nothing. lockup detection does not belong here */ mb();
should probably be made
while (!cpus_empty(flush_cpumask)) { cpu_relax(); /* nothing. lockup detection does not belong here */ mb(); }
(to have memory barrier directly before flush_cpumask is read).
Second, include/asm-i386/apic.h/apic_wait_icr_idle() does use cpu_relax(), but the version in asm-x86_64/ NOT! Is this because there's not much use doing cpu_relax() on SMP non-SMT machines, and x86_64 are always non-SMT? Or rather because someone screwed up?
And what about include/asm-i386/acpi.h/__acpi_acquire/release_global_lock()?
static inline int __acpi_acquire_global_lock (unsigned int *lock) { unsigned int old, new, val; do { old = *lock; new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1)); val = cmpxchg(lock, old, new); } while (unlikely (val != old)); return (new < 3) ? -1 : 0; }
could probably be made
static inline int __acpi_acquire_global_lock (unsigned int *lock) { unsigned int old, new, val; while (1) { old = *lock; new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1)); val = cmpxchg(lock, old, new); if (likely(val == old)) break; cpu_relax(); } return (new < 3) ? -1 : 0; }
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