Sean:
I understand that ops.poll_cq is actually ibv_cmd_poll_cq(), right ?
Do you mean during ibv_poll_cq() call, there is no system call involved
?
--CQ
> -----Original Message-----
> From: Sean Hefty [mailto:[email protected]]
> Sent: Wednesday, September 02, 2009 5:25 PM
> To: Tang, Changqing; [email protected]
> Cc: [email protected]
> Subject: RE: [ofa-general] performance to call ibv_poll_cq()
> vs. call select() on completion channel
>
> >But I just check the source code, ibv_poll_cq() is actually
> >ibv_cmd_poll_cq(), and ibv_cmd_poll_cq() calls write()
> system call on the IB device.
> >
> >Doesn't this write() system call switch to kernel mode and
> possiblely
> >casuse a context switch ?
>
> See verbs.h:
>
> static inline int ibv_poll_cq(struct ibv_cq *cq, int
> num_entries, struct ibv_wc
> *wc)
> {
> return cq->context->ops.poll_cq(cq, num_entries, wc); }
>
> The userspace provider library sets poll_cq to an internal call.
>
> - Sean
>
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