On Thu, Jul 25, 2019 at 05:18:08PM +0800, Ming Lei wrote:
> On Thu, Jul 25, 2019 at 04:35:30PM +0800, Bob Liu wrote:
> > On 7/25/19 4:26 PM, Ming Lei wrote:
> > > Spread queues among present CPUs first, then building the mapping
> > > on other non-present CPUs.
> > >
> > > So we can minimize count of dead queues which are mapped by un-present
> > > CPUs only. Then bad IO performance can be avoided by this unbalanced
> > > mapping between CPUs and queues.
> > >
> > > The similar policy has been applied on Managed IRQ affinity.
> > >
> > > Reported-by: Yi Zhang <yi.zhang@xxxxxxxxxx>
> > > Cc: Yi Zhang <yi.zhang@xxxxxxxxxx>
> > > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > > ---
> > > block/blk-mq-cpumap.c | 34 +++++++++++++++++++++++-----------
> > > 1 file changed, 23 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
> > > index f945621a0e8f..e217f3404dc7 100644
> > > --- a/block/blk-mq-cpumap.c
> > > +++ b/block/blk-mq-cpumap.c
> > > @@ -15,10 +15,9 @@
> > > #include "blk.h"
> > > #include "blk-mq.h"
> > >
> > > -static int cpu_to_queue_index(struct blk_mq_queue_map *qmap,
> > > - unsigned int nr_queues, const int cpu)
> > > +static int queue_index(struct blk_mq_queue_map *qmap, const int q)
> > > {
> > > - return qmap->queue_offset + (cpu % nr_queues);
> > > + return qmap->queue_offset + q;
> > > }
> > >
> > > static int get_first_sibling(unsigned int cpu)
> > > @@ -36,23 +35,36 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
> > > {
> > > unsigned int *map = qmap->mq_map;
> > > unsigned int nr_queues = qmap->nr_queues;
> > > - unsigned int cpu, first_sibling;
> > > + unsigned int cpu, first_sibling, q = 0;
> > > +
> > > + for_each_possible_cpu(cpu)
> > > + map[cpu] = -1;
> > > +
> > > + /*
> > > + * Spread queues among present CPUs first for minimizing
> > > + * count of dead queues which are mapped by all un-present CPUs
> > > + */
> > > + for_each_present_cpu(cpu) {
> > > + if (q >= nr_queues)
> > > + break;
> > > + map[cpu] = queue_index(qmap, q++);
> > > + }
> > >
> > > for_each_possible_cpu(cpu) {
> > > + if (map[cpu] != -1)
> > > + continue;
> > > /*
> > > * First do sequential mapping between CPUs and queues.
> > > * In case we still have CPUs to map, and we have some number of
> > > * threads per cores then map sibling threads to the same queue
> > > * for performance optimizations.
> > > */
> > > - if (cpu < nr_queues) {
> > > - map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
> >
> > Why not keep this similarly?
>
> Because the sequential mapping has been done already among present CPUs.
>
> >
> > > + first_sibling = get_first_sibling(cpu);
> > > + if (first_sibling == cpu) {
> > > + map[cpu] = queue_index(qmap, q);
> > > + q = (q + 1) % nr_queues;
> > > } else {
> > > - first_sibling = get_first_sibling(cpu);
> > > - if (first_sibling == cpu)
> > > - map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
> > > - else
> > > - map[cpu] = map[first_sibling];
> > > + map[cpu] = map[first_sibling];
> >
> > Then no need to share queue if nr_queues is enough for all possible cpu.
>
> I am not sure I follow your idea. There isn't 'enough' stuff wrt.
> nr_queues, which is just usually <= nr_queues.
The 2nd 'nr_queues' should have been 'nr_cpu_ids'.
thanks,
Ming
