xprtrdma: Invoke rpcrdma_reply_handler directly from RECV completion

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I noticed that the soft IRQ thread looked pretty busy under heavy
I/O workloads. perf suggested one area that was expensive was the
queue_work() call in rpcrdma_wc_receive. That gave me some ideas.

Instead of scheduling a separate worker to process RPC Replies,
promote the Receive completion handler to IB_POLL_WORKQUEUE, and
invoke rpcrdma_reply_handler directly.

Note that the poll workqueue is single-threaded. In order to keep
memory invalidation from serializing all RPC Replies, handle any
necessary invalidation tasks in a separate multi-threaded workqueue.

This provides a two-tier scheme, similar to OS I/O interrupt
handlers: A fast interrupt handler that schedules the slow handler
and re-enables the interrupt, and a slower handler that is invoked
for any needed heavy lifting.

Benefits include:
- One less context switch for RPCs that don't register memory
- Receive completion handling is moved out of soft IRQ context to
  make room for other users of soft IRQ
- The same CPU core now DMA syncs and XDR decodes the Receive buffer

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

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This commit is contained in:

Chuck Lever 2017-10-16 15:01:30 -04:00 • committed by Anna Schumaker

parent e1352c9610

commit d8f532d20e

3 changed files with 36 additions and 23 deletions

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44

net/sunrpc/xprtrdma/rpc_rdma.c

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8

net/sunrpc/xprtrdma/verbs.c

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5

net/sunrpc/xprtrdma/xprt_rdma.h

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