On Thu, Oct 30, 2014 at 06:28:13AM +0000, Elliott, Robert (Server Storage) wrote: > > > > -----Original Message----- > > From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi- > > owner@xxxxxxxxxxxxxxx] On Behalf Of Sudip Mukherjee > > Sent: Thursday, October 30, 2014 12:55 AM > > To: Fabian Frederick > > Cc: linux-kernel@xxxxxxxxxxxxxxx; Stephen M. Cameron; James E.J. > > Bottomley; iss_storagedev@xxxxxx; linux-scsi@xxxxxxxxxxxxxxx > > Subject: Re: [PATCH 1/1 linux-next] hpsa: remove set but unused variable > > rc > > > > On Wed, Oct 29, 2014 at 04:15:04PM +0100, Fabian Frederick wrote: > > > Fix -Wunused-but-set-variable warning > > > > you should also mention why you have left the call to > > irq_set_affinity_hint(). > > i am not sure , but it looks like irq_set_affinity_hint() is only > > checking if > > the lock is available or not. It is just locking ,then if lock is > > successfull then > > returning 0 or if lock fails then return -EINVAL, and unlocks before > > returnig. > > not doing anything else. > > > > thanks > > sudip > > No, that function sets a mask value that shows up in > /proc/irq/nnn/affinity_hint > that a program like irqbalance may use to set the CPU affinity mask > for each irq via > /proc/irq/nnn/smp_affinity (bitmap format) > /proc/irq/nnn/smp_affinity_list (range format) > > The reason is that in many cases, it is best when all these occur > on the same CPU that submitted the IO: > * LLD submission queues (if multiple are supported) > * LDD completion queues > * MSI-X interrupt indicating completion > * LLD completion interrupt handler > * block layer completion handler > > Benefits include: > * cache efficiency - the data structures for the IO aren't > pulled from CPU to CPU. > > * avoid IPI overhead in the block layer to get the completion > processed on the submitting CPU (which is done if using > rq_affinity=2 and the interrupt is routed to on another CPU). > > * self-throttle the CPUs - avoid swamping one CPU with > completion processing for IOs submitted by many other CPUs > (which leads to stalls on the victim and timeouts on the > aggressors). > > You must run irqbalance with an option to honor the hints; > some versions default to that, others don't. Or, disable > the irqbalance service and set them up the affinities > manually. > thanks , i think this is happening at desc->affinity_hint = m; thanks sudip > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
