On May 4, 2011, at 10:59 AM, Jeff Layton wrote:
> On Mon, 2 May 2011 21:40:08 -0400
> andros@xxxxxxxxxx wrote:
>
>> From: Andy Adamson <andros@xxxxxxxxxx>
>>
>> Hookup TCP congestion feedback into rpc_slot allocation so that the RPC layer
>> can fully utilize the negotiated TCP window.
>>
>> Use a slab cache for rpc_slots. Statically allocate an rpc_xprt rpc_slot slab
>> cache using GFP_KERNEL to the RPC_DEF_SLOT_TABLE number of slots at
>> rpc_xprt allocation.
>>
>> Add a dynamic rpc slot allocator to rpc_xprt_ops which is set only for TCP.
>> For TCP, trigger a dyamic slot allocation in response to a write_space
>> callback which is in turn called when the TCP layer is waiting for buffer space.
>>
>> Dynamically add a slot at the beginning of the RPC call_transmit state. The slot
>> allocator uses GFP_NOWAIT and will return without allocating a slot if
>> GFP_NOWAIT allocation fails. This is OK because the write_space callback will
>> be called again, and the dynamic slot allocator can retry.
>>
>> Signed-off-by: Andy Adamson <andros@xxxxxxxxx>
>> ---
>> include/linux/sunrpc/sched.h | 2 +
>> include/linux/sunrpc/xprt.h | 6 +++-
>> net/sunrpc/clnt.c | 4 ++
>> net/sunrpc/sched.c | 39 ++++++++++++++++++++++
>> net/sunrpc/xprt.c | 75 +++++++++++++++++++++++++++++++++++++-----
>> net/sunrpc/xprtsock.c | 1 +
>> 6 files changed, 117 insertions(+), 10 deletions(-)
>>
>
> [...]
>
>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>> index 9494c37..1b0aa55 100644
>> --- a/net/sunrpc/xprt.c
>> +++ b/net/sunrpc/xprt.c
>> @@ -498,6 +498,7 @@ void xprt_write_space(struct rpc_xprt *xprt)
>> dprintk("RPC: write space: waking waiting task on "
>> "xprt %p\n", xprt);
>> rpc_wake_up_queued_task(&xprt->pending, xprt->snd_task);
>> + set_bit(XPRT_WRITE_SPACE, &xprt->state);
>> }
>> spin_unlock_bh(&xprt->transport_lock);
>> }
>> @@ -957,6 +958,66 @@ static void xprt_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
>> spin_unlock(&xprt->reserve_lock);
>> }
>>
>
> Is the above a potential race as well? I looks possible (if unlikely)
> that we'd wake up the task, and it find that XPRT_WRITE_SPACE is still
> unset. Would it make more sense to do the set_bit call before waking up
> the task?
Yes - good catch.
-->Andy
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
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