Re: [PATCH V2 16/17] xprtrdma: Limit work done by completion handler

[Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On 4/22/2014 1:03 AM, Chuck Lever wrote:
> Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org> points out that a steady
> stream of CQ events could starve other work because of the boundless
> loop pooling in rpcrdma_{send,recv}_poll().
>
> Instead of a (potentially infinite) while loop, return after
> collecting a budgeted number of completions.
>
> Note that the total number of WCs that can be handled during one
> upcall is RPCRDMA_WC_BUDGET * 2, since the handler polls once before
> and once after re-enabling completion notifications.
>
> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
>
>   net/sunrpc/xprtrdma/verbs.c     |   10 ++++++----
>   net/sunrpc/xprtrdma/xprt_rdma.h |    1 +
>   2 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index abb8d8d..d46bdee 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -165,8 +165,9 @@ static int
>   rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
>   {
>   	struct ib_wc *wcs;
> -	int count, rc;
> +	int budget, count, rc;
>   
> +	budget = RPCRDMA_WC_BUDGET / RPCRDMA_POLLSIZE;
>   	do {
>   		wcs = ep->rep_send_wcs;
>   
> @@ -177,7 +178,7 @@ rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
>   		count = rc;
>   		while (count-- > 0)
>   			rpcrdma_sendcq_process_wc(wcs++);
> -	} while (rc == RPCRDMA_POLLSIZE);
> +	} while (rc == RPCRDMA_POLLSIZE && --budget);
>   	return 0;
>   }
>   
> @@ -254,8 +255,9 @@ static int
>   rpcrdma_recvcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
>   {
>   	struct ib_wc *wcs;
> -	int count, rc;
> +	int budget, count, rc;
>   
> +	budget = RPCRDMA_WC_BUDGET / RPCRDMA_POLLSIZE;
>   	do {
>   		wcs = ep->rep_recv_wcs;
>   
> @@ -266,7 +268,7 @@ rpcrdma_recvcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
>   		count = rc;
>   		while (count-- > 0)
>   			rpcrdma_recvcq_process_wc(wcs++);
> -	} while (rc == RPCRDMA_POLLSIZE);
> +	} while (rc == RPCRDMA_POLLSIZE && --budget);
>   	return 0;
>   }
>   
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index cb4c882..0c3b88e 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -74,6 +74,7 @@ struct rpcrdma_ia {
>    * RDMA Endpoint -- one per transport instance
>    */
>   
> +#define RPCRDMA_WC_BUDGET	(128)

Would be nice to be able to configure that (modparam perhaps?)

Other than that, looks OK.

Acked-by: Sagi Grimberg <sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>

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