On Wed, 2017-01-11 at 14:43 +0100, Johannes Thumshirn wrote: > I'd like to attend LSF/MM and would like to discuss polling for block > drivers. > > Currently there is blk-iopoll but it is neither as widely used as NAPI in > the networking field and accoring to Sagi's findings in [1] performance > with polling is not on par with IRQ usage. > > On LSF/MM I'd like to whether it is desirable to have NAPI like polling in > more block drivers and how to overcome the currently seen performance > issues. > > [1] http://lists.infradead.org/pipermail/linux-nvme/2016-October/006975.ht > ml
A typical Ethernet network adapter delays the generation of an interrupt after it has received a packet. A typical block device or HBA does not delay the generation of an interrupt that reports an I/O completion. I think that is why polling is more effective for network adapters than for block devices. I'm not sure whether it is possible to achieve benefits similar to NAPI for block devices without implementing interrupt coalescing in the block device firmware. Note: for block device implementations that use the RDMA API, the RDMA API supports interrupt coalescing (see also ib_modify_cq()). An example of the interrupt coalescing parameters for a network adapter: # ethtool -c em1 | grep -E 'rx-usecs:|tx-usecs:' rx-usecs: 3 tx-usecs: 0 Bart.-- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
