Hi Kashyap, On Fri, Feb 02, 2018 at 02:19:01PM +0530, Kashyap Desai wrote: > > > > > Today I am looking at one megaraid_sas related issue, and found > > > > > pci_alloc_irq_vectors(PCI_IRQ_AFFINITY) is used in the driver, so > > > > > looks each reply queue has been handled by more than one CPU if > > > > > there are more CPUs than MSIx vectors in the system, which is done > > > > > by generic irq affinity code, please see kernel/irq/affinity.c. > > > > > > Yes. That is a problematic area. If CPU and MSI-x(reply queue) is 1:1 > > > mapped, we don't have any issue. > > > > I guess the problematic area is similar with the following link: > > > > https://marc.info/?l=linux-kernel&m=151748144730409&w=2 > > Hi Ming, > > Above mentioned link is different discussion and looks like a generic > issue. megaraid_sas/mpt3sas will have same symptoms if irq affinity has > only offline CPUs. If you convert to SCSI_MQ/MQ, it is a generic issue, which is solved by a generic solution, otherwise now it is driver's responsibility to make sure to not use the reply queue in which no online CPUs is mapped. > Just for info - "In such condition, we can ask users to disable affinity > hit via module parameter " smp_affinity_enable". Yeah, that is exactly what I suggested to our QE friend. > > > > > otherwise could you explain a bit about the area? > > Please check below post for more details. > > https://marc.info/?l=linux-scsi&m=151601833418346&w=2 Seems SCSI_MQ/MQ can solve this issue, and I have replied on the above link, we can discuss on that thread further. thanks, Ming
