[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH RFC 4/4] xen: implement Xen-specific spinlocks
Johannes Weiner wrote: +static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; +static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);The plural is a bit misleading, as this is a single pointer per CPU. Yeah. And it's wrong because it's specifically *not* spinning, but blocking. +static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl) +{ + int cpu; + + for_each_online_cpu(cpu) {Would it be feasible to have a bitmap for the spinning CPUs in order to do a for_each_spinning_cpu() here instead? Or is setting a bit in spinning_lock() and unsetting it in unspinning_lock() more overhead than going over all CPUs here? Not worthwhile, I think. This is a very rare path: it will only happen if 1) there's lock contention, that 2) wasn't resolved within the timeout. In practice, this gets called a few thousand times per cpu over a kernbench, which is nothing. My very original version of this code kept a bitmask of interested CPUs within the lock, but there's only space for 24 cpus if we still use a byte for the lock itself. It all turned out fairly awkward, and this version is a marked improvement. J _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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