On Mon, May 18, 2020 at 04:16:05PM +0300, Yamin Friedman wrote:
>
> On 5/18/2020 11:30 AM, Leon Romanovsky wrote:
> > On Wed, May 13, 2020 at 02:52:41PM +0300, Yamin Friedman wrote:
> > > Allow a ULP to ask the core to provide a completion queue based on a
> > > least-used search on a per-device CQ pools. The device CQ pools grow in a
> > > lazy fashion when more CQs are requested.
> > >
> > > This feature reduces the amount of interrupts when using many QPs.
> > > Using shared CQs allows for more effcient completion handling. It also
> > > reduces the amount of overhead needed for CQ contexts.
> > >
> > > Test setup:
> > > Intel(R) Xeon(R) Platinum 8176M CPU @ 2.10GHz servers.
> > > Running NVMeoF 4KB read IOs over ConnectX-5EX across Spectrum switch.
> > > TX-depth = 32. The patch was applied in the nvme driver on both the target
> > > and initiator. Four controllers are accessed from each core. In the
> > > current test case we have exposed sixteen NVMe namespaces using four
> > > different subsystems (four namespaces per subsystem) from one NVM port.
> > > Each controller allocated X queues (RDMA QPs) and attached to Y CQs.
> > > Before this series we had X == Y, i.e for four controllers we've created
> > > total of 4X QPs and 4X CQs. In the shared case, we've created 4X QPs and
> > > only X CQs which means that we have four controllers that share a
> > > completion queue per core. Until fourteen cores there is no significant
> > > change in performance and the number of interrupts per second is less than
> > > a million in the current case.
> > > ==================================================
> > > |Cores|Current KIOPs |Shared KIOPs |improvement|
> > > |-----|---------------|--------------|-----------|
> > > |14 |2332 |2723 |16.7% |
> > > |-----|---------------|--------------|-----------|
> > > |20 |2086 |2712 |30% |
> > > |-----|---------------|--------------|-----------|
> > > |28 |1971 |2669 |35.4% |
> > > |=================================================
> > > |Cores|Current avg lat|Shared avg lat|improvement|
> > > |-----|---------------|--------------|-----------|
> > > |14 |767us |657us |14.3% |
> > > |-----|---------------|--------------|-----------|
> > > |20 |1225us |943us |23% |
> > > |-----|---------------|--------------|-----------|
> > > |28 |1816us |1341us |26.1% |
> > > ========================================================
> > > |Cores|Current interrupts|Shared interrupts|improvement|
> > > |-----|------------------|-----------------|-----------|
> > > |14 |1.6M/sec |0.4M/sec |72% |
> > > |-----|------------------|-----------------|-----------|
> > > |20 |2.8M/sec |0.6M/sec |72.4% |
> > > |-----|------------------|-----------------|-----------|
> > > |28 |2.9M/sec |0.8M/sec |63.4% |
> > > ====================================================================
> > > |Cores|Current 99.99th PCTL lat|Shared 99.99th PCTL lat|improvement|
> > > |-----|------------------------|-----------------------|-----------|
> > > |14 |67ms |6ms |90.9% |
> > > |-----|------------------------|-----------------------|-----------|
> > > |20 |5ms |6ms |-10% |
> > > |-----|------------------------|-----------------------|-----------|
> > > |28 |8.7ms |6ms |25.9% |
> > > |===================================================================
> > >
> > > Performance improvement with sixteen disks (sixteen CQs per core) is
> > > comparable.
> > >
> > > Signed-off-by: Yamin Friedman <yaminf@xxxxxxxxxxxx>
> > > Reviewed-by: Or Gerlitz <ogerlitz@xxxxxxxxxxxx>
> > > Reviewed-by: Max Gurtovoy <maxg@xxxxxxxxxxxx>
> > > ---
> > > drivers/infiniband/core/core_priv.h | 4 ++
> > > drivers/infiniband/core/cq.c | 137 ++++++++++++++++++++++++++++++++++++
> > > drivers/infiniband/core/device.c | 2 +
> > > include/rdma/ib_verbs.h | 35 +++++++++
> > > 4 files changed, 178 insertions(+)
> > >
> > > diff --git a/drivers/infiniband/core/core_priv.h b/drivers/infiniband/core/core_priv.h
> > > index cf42acc..fa3151b 100644
> > > --- a/drivers/infiniband/core/core_priv.h
> > > +++ b/drivers/infiniband/core/core_priv.h
> > > @@ -414,4 +414,8 @@ void rdma_umap_priv_init(struct rdma_umap_priv *priv,
> > > struct vm_area_struct *vma,
> > > struct rdma_user_mmap_entry *entry);
> > >
> > > +void ib_cq_pool_init(struct ib_device *dev);
> > > +
> > > +void ib_cq_pool_destroy(struct ib_device *dev);
> > > +
> > > #endif /* _CORE_PRIV_H */
> > > diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c
> > > index 04046eb..5319c14 100644
> > > --- a/drivers/infiniband/core/cq.c
> > > +++ b/drivers/infiniband/core/cq.c
> > > @@ -7,7 +7,11 @@
> > > #include <linux/slab.h>
> > > #include <rdma/ib_verbs.h>
> > >
> > > +#include "core_priv.h"
> > > +
> > > #include <trace/events/rdma_core.h>
> > > +/* Max size for shared CQ, may require tuning */
> > > +#define IB_MAX_SHARED_CQ_SZ 4096
> > >
> > > /* # of WCs to poll for with a single call to ib_poll_cq */
> > > #define IB_POLL_BATCH 16
> > > @@ -218,6 +222,7 @@ struct ib_cq *__ib_alloc_cq_user(struct ib_device *dev, void *private,
> > > cq->cq_context = private;
> > > cq->poll_ctx = poll_ctx;
> > > atomic_set(&cq->usecnt, 0);
> > > + cq->comp_vector = comp_vector;
> > >
> > > cq->wc = kmalloc_array(IB_POLL_BATCH, sizeof(*cq->wc), GFP_KERNEL);
> > > if (!cq->wc)
> > > @@ -304,6 +309,8 @@ static void _ib_free_cq_user(struct ib_cq *cq, struct ib_udata *udata)
> > > {
> > > if (WARN_ON_ONCE(atomic_read(&cq->usecnt)))
> > > return;
> > > + if (WARN_ON_ONCE(cq->cqe_used != 0))
> > Let's do WARN_ON_ONCE(cq->cqe_used)
> >
> > > + return;
> > >
> > > switch (cq->poll_ctx) {
> > > case IB_POLL_DIRECT:
> > > @@ -340,3 +347,133 @@ void ib_free_cq_user(struct ib_cq *cq, struct ib_udata *udata)
> > > _ib_free_cq_user(cq, udata);
> > > }
> > > EXPORT_SYMBOL(ib_free_cq_user);
> > > +
> > > +void ib_cq_pool_init(struct ib_device *dev)
> > > +{
> > > + int i;
> > > +
> > > + spin_lock_init(&dev->cq_pools_lock);
> > > + for (i = 0; i < ARRAY_SIZE(dev->cq_pools); i++)
> > > + INIT_LIST_HEAD(&dev->cq_pools[i]);
> > > +}
> > > +
> > > +void ib_cq_pool_destroy(struct ib_device *dev)
> > > +{
> > > + struct ib_cq *cq, *n;
> > > + int i;
> > > +
> > > + for (i = 0; i < ARRAY_SIZE(dev->cq_pools); i++) {
> > > + list_for_each_entry_safe(cq, n, &dev->cq_pools[i], pool_entry)
> > > + _ib_free_cq_user(cq, NULL);
> > > + }
> > > +
> > > +}
> > > +
> > > +static int ib_alloc_cqs(struct ib_device *dev, int nr_cqes,
> > > + enum ib_poll_context poll_ctx)
> > > +{
> > > + LIST_HEAD(tmp_list);
> > > + struct ib_cq *cq;
> > > + unsigned long flags;
> > > + int nr_cqs, ret, i;
> > > +
> > > + /*
> > > + * Allocated at least as many CQEs as requested, and otherwise
> > > + * a reasonable batch size so that we can share CQs between
> > > + * multiple users instead of allocating a larger number of CQs.
> > > + */
> > > + nr_cqes = min(dev->attrs.max_cqe, max(nr_cqes, IB_MAX_SHARED_CQ_SZ));
> > > + nr_cqs = min_t(int, dev->num_comp_vectors, num_online_cpus());
> > > + for (i = 0; i < nr_cqs; i++) {
> > > + cq = ib_alloc_cq(dev, NULL, nr_cqes, i, poll_ctx);
> > > + if (IS_ERR(cq)) {
> > > + ret = PTR_ERR(cq);
> > > + goto out_free_cqs;
> > > + }
> > > + cq->shared = true;
> > > + list_add_tail(&cq->pool_entry, &tmp_list);
> > > + }
> > > +
> > > + spin_lock_irqsave(&dev->cq_pools_lock, flags);
> > > + list_splice(&tmp_list, &dev->cq_pools[poll_ctx - 1]);
> > > + spin_unlock_irqrestore(&dev->cq_pools_lock, flags);
> > > +
> > > + return 0;
> > > +
> > > +out_free_cqs:
> > > + list_for_each_entry(cq, &tmp_list, pool_entry)
> > > + ib_free_cq(cq);
> > > + return ret;
> > > +}
> > > +
> > > +struct ib_cq *ib_cq_pool_get(struct ib_device *dev, unsigned int nr_cqe,
> > > + int comp_vector_hint,
> > > + enum ib_poll_context poll_ctx)
> > > +{
> > > + static unsigned int default_comp_vector;
> > > + int vector, ret, num_comp_vectors;
> > > + struct ib_cq *cq, *found = NULL;
> > > + unsigned long flags;
> > > +
> > > + if (poll_ctx > ARRAY_SIZE(dev->cq_pools) || poll_ctx == IB_POLL_DIRECT)
> > > + return ERR_PTR(-EINVAL);
> > > +
> > > + num_comp_vectors = min_t(int, dev->num_comp_vectors,
> > > + num_online_cpus());
> > > + /* Project the affinty to the device completion vector range */
> > > + if (comp_vector_hint < 0)
> > > + vector = default_comp_vector++ % num_comp_vectors;
> > > + else
> > > + vector = comp_vector_hint % num_comp_vectors;
> > > +
> > > + /*
> > > + * Find the least used CQ with correct affinity and
> > > + * enough free CQ entries
> > > + */
> > > + while (!found) {
> > > + spin_lock_irqsave(&dev->cq_pools_lock, flags);
> > > + list_for_each_entry(cq, &dev->cq_pools[poll_ctx - 1],
> > > + pool_entry) {
> > > + if (vector != cq->comp_vector)
> > I think that this check worth to have a comment.
> > At least for me, it is not clear if it will work correctly if
> > comp_vector == 0.
> >
> > > + continue;
> > > + if (cq->cqe_used + nr_cqe > cq->cqe)
> > > + continue;
> > > + if (found && cq->cqe_used >= found->cqe_used)
> > > + continue;
> > > + found = cq;
> > > + break;
> > > + }
> > > +
> > > + if (found) {
> > > + found->cqe_used += nr_cqe;
> > > + spin_unlock_irqrestore(&dev->cq_pools_lock, flags);
> > > +
> > > + return found;
> > > + }
> > > + spin_unlock_irqrestore(&dev->cq_pools_lock, flags);
> > > +
> > > + /*
> > > + * Didn't find a match or ran out of CQs in the device
> > > + * pool, allocate a new array of CQs.
> > > + */
> > > + ret = ib_alloc_cqs(dev, nr_cqe, poll_ctx);
> > > + if (ret)
> > > + return ERR_PTR(ret);
> > > + }
> > > +
> > > + return found;
> > > +}
> > > +EXPORT_SYMBOL(ib_cq_pool_get);
> > > +
> > > +void ib_cq_pool_put(struct ib_cq *cq, unsigned int nr_cqe)
> > > +{
> > > + unsigned long flags;
> > > +
> > > + if (nr_cqe > cq->cqe_used)
> > > + return;
> > Is it possible?
> > 1. It is racy
> > 2. It is a bug in the ib_cq_pool_put() caller.
>
> It is possible, the pool doesn't save the amount of cqes used per user.
So, #2 from the list above.
>
> I think to make it really secure I would have to never reduce the cqes used,
> save the number of active users, and have some form of garbage collection
> for used up CQs but that seems to me a lot for something that should not
> occur during proper use.
>
> Would it be better to just have a WARN for this case?
I think so.
Thanks
