Hi-
I'm on a "mission" to reduce the amount of page allocator churn
that happens during server-side RPC call processing.
In the case where svcrdma needs to perform an RDMA Read to pull
Read chunks from a client, currently two calls to svc_rdma_recvfrom
are necessary:
Call 1:
An ingress Receive is processed. If there are Read chunks, the
transport strips the pages out of the passed-in svc_rqst, sets up
the RDMA Read with those pages and posts the Read, then returns
the svc_rqst with missing pages. Return value of zero means no
RPC Call is ready yet.
---
Meanwhile svc has to refill those pages in the svc_rqst to
prepare it for the next incoming RPC.
---
Call 2:
The Read completion has occurred. The transport strips the pages
out of the passed-in svc_rqst and frees them. It copies the
pages from the Read sink buffer into the svc_rqst, and returns
the completed RPC.
---
Instead, let's do the RDMA Reads synchronously with a single call to
svc_rdma_recvfrom(). When svc_rdma_recvfrom() handles an ingress
Receive with Read chunks, set up the RDMA Read sink buffer using the
available pages in the svc_rqst, and wait right there for
completion.
For large Read chunks, this avoids freeing a bunch of pages and then
allocating them again. Fewer trips to the page allocator means less
time with IRQs disabled, and measurably faster turn-around for the
next RPC.
Also, now that XPT_BUSY is cleared immediately when a Receive is
dequeued, the transport can handle a higher rate of incoming RPCs.
---
Chuck Lever (6):
SUNRPC: Export svc_xprt_received()
SUNRPC: Move svc_xprt_received() call sites
svcrdma: Single-stage RDMA Read
svcrdma: Remove sc_read_complete_q
svcrdma: Remove svc_rdma_recv_ctxt::rc_pages and ::rc_arg
svcrdma: Clean up dto_q critical section in svc_rdma_recvfrom()
include/linux/sunrpc/svc_rdma.h | 5 --
net/sunrpc/svc_xprt.c | 7 +-
net/sunrpc/svcsock.c | 9 +-
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 76 +++-------------
net/sunrpc/xprtrdma/svc_rdma_rw.c | 108 ++++++++---------------
net/sunrpc/xprtrdma/svc_rdma_transport.c | 1 -
6 files changed, 60 insertions(+), 146 deletions(-)
--
Chuck Lever
