On Wed, Jun 24, 2015 at 10:34 PM, Akinobu Mita <akinobu.m...@gmail.com> wrote: > Hi Ming, > > 2015-06-24 18:46 GMT+09:00 Ming Lei <tom.leim...@gmail.com>: >> On Sun, Jun 21, 2015 at 9:52 PM, Akinobu Mita <akinobu.m...@gmail.com> wrote: >>> ctx->index_hw is zero for the CPUs which have never been onlined since >>> the block queue was initialized. If one of those CPUs is hotadded and >>> starts handling request before new mappings are established, pending >> >> Could you explain a bit what the handling request is? The fact is that >> blk_mq_queue_reinit() is run after all queues are put into freezing. > > Notifier callbacks for CPU_ONLINE action can be run on the other CPU > than the CPU which was just onlined. So it is possible for the > process running on the just onlined CPU to insert request and run > hw queue before blk_mq_queue_reinit_notify() is actually called with > action=CPU_ONLINE.
You are right because blk_mq_queue_reinit_notify() is alwasy run after the CPU becomes UP, so there is a tiny window in which the CPU is up but the mapping is updated. Per current design, the CPU just onlined is still mapped to hw queue 0 until the mapping is updated by blk_mq_queue_reinit_notify(). But I am wondering why it is a problem and why you think flush_busy_ctxs can't find the requests on the software queue in this situation? -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
