On 02/28/2018 11:42 PM, jianchao.wang wrote: > Hi Keith > > Thanks for your kindly response and directive > > On 02/28/2018 11:27 PM, Keith Busch wrote: >> On Wed, Feb 28, 2018 at 10:53:31AM +0800, jianchao.wang wrote: >>> On 02/27/2018 11:13 PM, Keith Busch wrote: >>>> On Tue, Feb 27, 2018 at 04:46:17PM +0800, Jianchao Wang wrote: >>>>> Currently, adminq and ioq0 share the same irq vector. This is >>>>> unfair for both amdinq and ioq0. >>>>> - For adminq, its completion irq has to be bound on cpu0. >>>>> - For ioq0, when the irq fires for io completion, the adminq irq >>>>> action has to be checked also. >>>> >>>> This change log could use some improvements. Why is it bad if admin >>>> interrupts affinity is with cpu0? >>> >>> adminq interrupts should be able to fire everywhere. >>> do we have any reason to bound it on cpu0 ? >> >> Your patch will have the admin vector CPU affinity mask set to >> 0xff..ff. The first set bit for an online CPU is the one the IRQ handler >> will run on, so the admin queue will still only run on CPU 0. > > hmmm...yes. > When I test there is only one irq vector, I get following result: > 124: 0 0 253541 0 0 0 > 0 0 IR-PCI-MSI 1048576-edge nvme0q0, nvme0q1 >
the irqbalance may migrate the adminq irq away from cpu0. >> >>>> Are you able to measure _any_ performance difference on IO queue 1 vs IO >>>> queue 2 that you can attribute to IO queue 1's sharing vector 0? >>> >>> Actually, I didn't get any performance improving on my own NVMe card. >>> But it may be needed on some enterprise card, especially the media is >>> persist memory. >>> nvme_irq will be invoked twice when ioq0 irq fires, this will introduce >>> another unnecessary DMA >>> accessing on cq entry. >> >> A CPU reading its own memory isn't a DMA. It's just a cheap memory read. > > Oh sorry, my bad, I mean it is operation on DMA address, it is uncached. > nvme_irq > -> nvme_process_cq > -> nvme_read_cqe > -> nvme_cqe_valid > > static inline bool nvme_cqe_valid(struct nvme_queue *nvmeq, u16 head, > u16 phase) > { > return (le16_to_cpu(nvmeq->cqes[head].status) & 1) == phase; > } > > Sincerely > Jianchao >