On Wed, 2017-07-12 at 10:30 +0800, Ming Lei wrote: > On Tue, Jul 11, 2017 at 12:25:16PM -0600, Jens Axboe wrote: > > What happens with fluid congestion boundaries, with shared tags? > > The approach in this patch should work, but the threshold may not > be accurate in this way, one simple method is to use the average > tag weight in EWMA, like this: > > sbitmap_weight() / hctx->tags->active_queues Hello Ming, That approach would result in a severe performance degradation. "active_queues" namely represents the number of queues against which I/O ever has been queued. If e.g. 64 LUNs would be associated with a single SCSI host and all 64 LUNs are responding and if the queue depth would also be 64 then the approach you proposed will reduce the effective queue depth per LUN from 64 to 1. Bart.
