> On Nov 23, 2015, at 7:39 PM, Tom Talpey <tom@xxxxxxxxxx> wrote:
>
> On 11/23/2015 5:20 PM, Chuck Lever wrote:
>> Extra resources for handling backchannel requests have to be
>> pre-allocated when a transport instance is created. Set a limit.
>>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> include/linux/sunrpc/svc_rdma.h | 5 +++++
>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 6 +++++-
>> 2 files changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>> index f869807..478aa30 100644
>> --- a/include/linux/sunrpc/svc_rdma.h
>> +++ b/include/linux/sunrpc/svc_rdma.h
>> @@ -178,6 +178,11 @@ struct svcxprt_rdma {
>> #define RPCRDMA_SQ_DEPTH_MULT 8
>> #define RPCRDMA_MAX_REQUESTS 32
>> #define RPCRDMA_MAX_REQ_SIZE 4096
>> +#if defined(CONFIG_SUNRPC_BACKCHANNEL)
>
> Why is this a config option? Why wouldn't you always want
> this? It's needed for any post-1990 NFS dialect.
I think some distros want to be able to compile out NFSv4.x
on small systems, and take all the backchannel cruft with it.
>> +#define RPCRDMA_MAX_BC_REQUESTS 8
>
> Why a constant 8? The forward channel value is apparently
> configurable, just a few lines down.
The client side backward direction credit limit, now
in 4.4, is already a constant.
The client side ULP uses a constant for the slot table
size: NFS4_MAX_BACK_CHANNEL_OPS. I’m not 100% sure but
the server seems to just echo that number back to the
client.
I’d rather not add an admin knob for this. Why would it
be necessary?
>> +#else
>> +#define RPCRDMA_MAX_BC_REQUESTS 0
>> +#endif
>>
>> #define RPCSVC_MAXPAYLOAD_RDMA RPCSVC_MAXPAYLOAD
>>
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> index b348b4a..01c7b36 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> @@ -923,8 +923,10 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>> (size_t)RPCSVC_MAXPAGES);
>> newxprt->sc_max_sge_rd = min_t(size_t, devattr.max_sge_rd,
>> RPCSVC_MAXPAGES);
>> + /* XXX: what if HCA can't support enough WRs for bc operation? */
>> newxprt->sc_max_requests = min((size_t)devattr.max_qp_wr,
>> - (size_t)svcrdma_max_requests);
>> + (size_t)(svcrdma_max_requests +
>> + RPCRDMA_MAX_BC_REQUESTS));
>> newxprt->sc_sq_depth = RPCRDMA_SQ_DEPTH_MULT * newxprt->sc_max_requests;
>>
>> /*
>> @@ -964,7 +966,9 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>> qp_attr.event_handler = qp_event_handler;
>> qp_attr.qp_context = &newxprt->sc_xprt;
>> qp_attr.cap.max_send_wr = newxprt->sc_sq_depth;
>> + qp_attr.cap.max_send_wr += RPCRDMA_MAX_BC_REQUESTS;
>> qp_attr.cap.max_recv_wr = newxprt->sc_max_requests;
>> + qp_attr.cap.max_recv_wr += RPCRDMA_MAX_BC_REQUESTS;
>> qp_attr.cap.max_send_sge = newxprt->sc_max_sge;
>> qp_attr.cap.max_recv_sge = newxprt->sc_max_sge;
>> qp_attr.sq_sig_type = IB_SIGNAL_REQ_WR;
>>
>> --
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>>
>>
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--
Chuck Lever
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