On Tue, Aug 14, 2018 at 06:09:19PM +0300, Yishai Hadas wrote:
> From: Artemy Kovalyov <artemyko@xxxxxxxxxxxx>
>
> When regular CQ attempts to generate a CQE and the CQ is already full
> overflow occurs and async error is generated.
> On CQ created with IBV_CREATE_CQ_ATTR_IGNORE_OVERRUN flag overflow check
> is disabled, error is never generated and CQE always will be written to
> next entry.
> Shortening fast-path message receive treatment allows low-latency
> application to achieve better performance.
>
> Signed-off-by: Artemy Kovalyov <artemyko@xxxxxxxxxxxx>
> Signed-off-by: Yishai Hadas <yishaih@xxxxxxxxxxxx>
> libibverbs/cmd_cq.c | 3 +++
> libibverbs/man/ibv_create_cq_ex.3 | 1 +
> libibverbs/verbs.h | 1 +
> 3 files changed, 5 insertions(+)
>
> diff --git a/libibverbs/cmd_cq.c b/libibverbs/cmd_cq.c
> index 73cd2f2..7669518 100644
> +++ b/libibverbs/cmd_cq.c
> @@ -142,6 +142,9 @@ int ibv_cmd_create_cq_ex(struct ibv_context *context,
> if (cq_attr->wc_flags & IBV_WC_EX_WITH_COMPLETION_TIMESTAMP)
> flags |= IB_UVERBS_CQ_FLAGS_TIMESTAMP_COMPLETION;
>
> + if (cq_attr->flags & IBV_CREATE_CQ_ATTR_IGNORE_OVERRUN)
> + flags |= IB_UVERBS_CQ_FLAGS_IGNORE_OVERRUN;
> +
> return ibv_icmd_create_cq(context, cq_attr->cqe, cq_attr->channel,
> cq_attr->comp_vector, flags,
> ibv_cq_ex_to_cq(cq), cmdb);
> diff --git a/libibverbs/man/ibv_create_cq_ex.3 b/libibverbs/man/ibv_create_cq_ex.3
> index 2abdbe4..5d39457 100644
> +++ b/libibverbs/man/ibv_create_cq_ex.3
> @@ -52,6 +52,7 @@ enum ibv_cq_init_attr_mask {
>
> enum ibv_create_cq_attr_flags {
> IBV_CREATE_CQ_ATTR_SINGLE_THREADED = 1 << 0, /* This CQ is used from a single threaded, thus no locking is required */
> + IBV_CREATE_CQ_ATTR_IGNORE_OVERRUN = 1 << 1, /* This CQ will not pass to error state if overrun, CQE always will be written to next entry */
> };
This really needs a longer man page discussion. What exactly happens
at overflow? Does the CQ continue to work? Does it become corrupted?
Are CQEs just lost?
How should an application recover?
Probably stress that an application must be designed to avoid ever
overflowing the CQ.
Jason
