On Tue, Aug 14, 2018 at 09:29:25AM +0800, jianchao.wang wrote: > Hi Ming > > On 08/13/2018 06:48 PM, Ming Lei wrote: > > It is nothing to do with where the admin request is sent, so no any > > difference wrt. this issue between with and without this patchset, > > right? > > I'm afraid not. > > For example: > A scsi host has 8 LUNs associated with it. > Before this patch set, > When we send out the admin command, the budget is _per_ LUN, 1/8 of the total tags. > After this patch set, > When we send out the admin command, the budget is equal to _one_ LUN, 1/8 of the total tags. > > However, the 1/8 above is different. > Before the patch set, every LUN's admin command has 1/8 budget to use which is per LUN. Strictly speaking, it is that all admin command and all other IOs share the 1/8 budget if they aimed at same LUN. > After this patch set, all the 8 LUNs admin command has to share the 1/8 budget. That only means number of active admin commands won't be bigger than 1/8 budget, which is one extra implicit limit on admin queue. However, other LUN's budget is still 1/8. So performance for IO queue won't be affected at all, will it? scsi_execute_* can't be called often, it is really in slow path, so I don't think there is any possible performance effect with this patch, or do you have other performance concern wrt. this patch? We still have q->queue_depth for enhancing any limit for admin queue, but up to now, not see it is necessary. Thanks, Ming
