[PATCH] rdma: Fix multiple disk performance degradation

[Philipp Reisner]

Hi Zhengbing,

That patch looks interesting.
Please allow me a few days for a proper repyl. Currently, I am at a conference.

best regards,
 Philipp

On Sat, Sep 14, 2024 at 8:12 AM zhengbing.huang
<zhengbing.huang at easystack.cn> wrote:
>
> In the performance test of rdma mode, we found that when
> two drbd disks were simultaneously subjected to high-pressure I/O write,
> the IOPS of each drbd disk would be reduced by half.
>
> The reason is that if the cq_attr.comp_vector parameter
> is not specified when rdma create send_cq and recv_cq,
> cq will be allocated to the same irq for processing.
> At this point, if multiple disks are stress tested at the same time,
> irq will not be processed in a timely manner
> and performance will decrease.
>
> The solution is to use the network port number as the index of the comp_vector,
> so that the cq of each disk can be distributed across different IRQs
>
> Signed-off-by: zhengbing.huang <zhengbing.huang at easystack.cn>
> ---
>  drbd/drbd_transport_rdma.c | 44 ++++++++++++++++++++++++++++++++++----
>  1 file changed, 40 insertions(+), 4 deletions(-)
>
> diff --git a/drbd/drbd_transport_rdma.c b/drbd/drbd_transport_rdma.c
> index 813787c28..8915e60d1 100644
> --- a/drbd/drbd_transport_rdma.c
> +++ b/drbd/drbd_transport_rdma.c
> @@ -2486,10 +2486,43 @@ static int dtr_init_flow(struct dtr_path *path, enum drbd_stream stream)
>         return err;
>  }
>
> +static int dtr_get_my_port(struct dtr_path *path)
> +{
> +       int port = 0;
> +       struct sockaddr_storage *addr = (struct sockaddr_storage *)&path->path.my_addr;
> +
> +       if (addr->ss_family == AF_INET6) {
> +               const struct sockaddr_in6 *v6a = (const struct sockaddr_in6 *)addr;
> +
> +               port = be16_to_cpu(v6a->sin6_port);
> +       } else /* AF_INET, AF_SSOCKS, AF_SDP */ {
> +               const struct sockaddr_in *v4a = (const struct sockaddr_in *)addr;
> +
> +               port = be16_to_cpu(v4a->sin_port);
> +       }
> +
> +       return port;
> +}
> +
> +static void dtr_get_comp_vectors(struct dtr_path *path, int cq_num, int *comp_vectors)
> +{
> +       int i;
> +       int tmp_comp_vector = dtr_get_my_port(path) * cq_num;
> +
> +       for (i = 0; i < cq_num; i++) {
> +               comp_vectors[i] = tmp_comp_vector + i;
> +       }
> +
> +       return;
> +}
> +
>  static int _dtr_cm_alloc_rdma_res(struct dtr_cm *cm,
>                                     enum dtr_alloc_rdma_res_causes *cause)
>  {
> -       int err, i, rx_descs_max = 0, tx_descs_max = 0;
> +       int err, i, cq_index = 0, rx_descs_max = 0, tx_descs_max = 0;
> +       int cq_num = 2; /* recv_cq and send_cq */
> +       int comp_vectors[2] = {0}; /* recv_cq and send_cq */
> +       struct ib_device *device = cm->id->device;
>         struct ib_cq_init_attr cq_attr = {};
>         struct dtr_path *path = cm->path;
>
> @@ -2504,16 +2537,18 @@ static int _dtr_cm_alloc_rdma_res(struct dtr_cm *cm,
>         /* in 4.9 ib_alloc_pd got the ability to specify flags as second param */
>         /* so far we don't use flags, but if we start using them, we have to be
>          * aware that the compat layer removes this parameter for old kernels */
> -       cm->pd = ib_alloc_pd(cm->id->device, 0);
> +       cm->pd = ib_alloc_pd(device, 0);
>         if (IS_ERR(cm->pd)) {
>                 *cause = IB_ALLOC_PD;
>                 err = PTR_ERR(cm->pd);
>                 goto pd_failed;
>         }
>
> +       dtr_get_comp_vectors(path, cq_num, comp_vectors);
>         /* create recv completion queue (CQ) */
>         cq_attr.cqe = rx_descs_max;
> -       cm->recv_cq = ib_create_cq(cm->id->device,
> +       cq_attr.comp_vector = comp_vectors[cq_index] % device->num_comp_vectors;
> +       cm->recv_cq = ib_create_cq(device,
>                         dtr_rx_cq_event_handler, NULL, cm,
>                         &cq_attr);
>         if (IS_ERR(cm->recv_cq)) {
> @@ -2524,7 +2559,8 @@ static int _dtr_cm_alloc_rdma_res(struct dtr_cm *cm,
>
>         /* create send completion queue (CQ) */
>         cq_attr.cqe = tx_descs_max;
> -       cm->send_cq = ib_create_cq(cm->id->device,
> +       cq_attr.comp_vector = comp_vectors[cq_index++] % device->num_comp_vectors;
> +       cm->send_cq = ib_create_cq(device,
>                         dtr_tx_cq_event_handler, NULL, cm,
>                         &cq_attr);
>         if (IS_ERR(cm->send_cq)) {
> --
> 2.17.1
>