On Fri, Apr 08, 2016 at 01:40:06PM -0400, Matthew Wilcox wrote: > - Inability to use all queues supported by a device. Intel's P3700 > supports 31 queues, but block-mq insists on assigning an even multiple > of CPUs to each queue. So if you have 48 CPUs, it will use 24 queues. > If you have 128 CPUs, it will only use 16 of the queues. While it'd be better to use all the available h/w resources, that's actually not the worst part. The real problems occur when there are more physical/unique CPUs than h/w queues since blk-mq does not consider CPU topology beyond thread siblings. With 128 CPUs, blk-mq may use all 31 queues P3700 supports, but many CPU groups won't share a last-level-cache. Smarter assignment would reclaim some untapped performance, and we can share such code prior to the session. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
