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Subject: Re: [OMPI devel] [ofa-general] uDAPL EVD queue length issue
From: Arlin Davis (ardavis_at_[hidden])
Date: 2007-12-05 12:57:53


>>
>> I'm running OFED 1.2.5 and using Chelsio.
>>
> From the linux rdma verbs perspective, ibv_create_cq() will create a cq
> that is >= the requested depth. The fact that mthca always bumps the
> size up to the next power of 2 isn't something udapl can rely on.

It doesn't.

uDAPL passes the users requested qlen directly to the verbs
ibv_create_cq call (dapl_openib_cq.c) and then uses the returned qlen to
allocate EVD's (dapl_evd_util.c) and a ring buffer
(dapl_ring_buffer_util.c) for managing the free and pending events.

The EVD's are allocated based on returned qlen from verbs and the
ring_buffer is allocated based on qlen, next power of 2 minus 1. Unless
I am missing something, I don't see how we can get less then what is
requested.

>
> Here's the crux: If creating a udapl evd of 256 results in a cq of 256
> and the udapl returns a evd with size 255, then udapl is broken...

Yes, I agree. But I don't see how this is happening.

Here is output from my dtest when requesting 256 and verbs returning the
same qlen. You can see before and after verbs we get 256, the rbufs are
511, and the query EVD call returns 256 to the user.

  cq_object_create: (0x519bb0,0x519d00)
dapls_ib_cq_alloc: evd 0x519bb0 cqlen=256
dapls_ib_cq_alloc: new_cq 0x519d60 cqlen=256
  setup_async_cb: ia 0x518270 type 2 hdl 0x519bb0 cb 0x2a957c8e70 ctx
0x519bb0
>>> rbuf_alloc: size 256 rsize 511
>>> rbuf_alloc: size 256 rsize 511
dapl_evd_create () returns 0x0

9920 dto_req_evd QLEN - requested 256 and actual 256
9920 Create events done

Can you turn up DAPL debug(DAPL_DBG_TYPE=0xffff) so I can see what is
happening?

Thanks,

-arlin