On 7/18/2017 10:36 AM, Keith Busch wrote: > On Mon, Jul 17, 2017 at 07:07:00PM -0400, okaya@xxxxxxxxxxxxxx wrote: >> Maybe, I need to understand the design better. I was curious why completion >> and submission queues were protected by a single lock causing lock >> contention. > Ideally the queues are tied to CPUs, so you couldn't have one thread > submitting to a particular queue-pair while another thread is reaping > completions from it. Such a setup wouldn't get lock contention. I do see that the NVMe driver is creating a completion interrupt on each CPU core for the completions. No problems with that. However, I don't think you can guarantee that there will always be a single CPU core targeting one submission queue especially with asynchronous IO. Lock contention counters from CONFIG_LOCK_STAT are pointing to nvmeq->lock in my FIO tests. Did I miss something? > > Some machines have so many CPUs, though, that sharing hardware queues > is required. We've experimented with separate submission and completion > locks for such cases, but I've never seen an improved performance as a > result. > I have also experimented with multiple locks with no significant gains. However, I was curious if somebody else had a better implementation than mine. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
