[ofa-general] performance to call ibv_poll_cq() vs. call select() on completion channel

[Tang, Changqing]

I did not understand the relation between ops.poll_cq() and ibv_cmd_poll_cq() correctly.

It is clear now.

Thank you.

--CQ


> -----Original Message-----
> From: Roland Dreier [mailto:rdreier at cisco.com] 
> Sent: Wednesday, September 02, 2009 6:09 PM
> To: Tang, Changqing
> Cc: Sean Hefty; tziporet at dev.mellanox.co.il; 
> general at lists.openfabrics.org
> Subject: Re: [ofa-general] performance to call ibv_poll_cq() 
> vs. call select() on completion channel
> 
> 
>  > 	I understand that ops.poll_cq is actually 
> ibv_cmd_poll_cq(), right ?
> 
> No, not for most devices.  Look at libmthca, etc to see what 
> the poll_cq method is set to.
> 
>  > 	Do you mean during ibv_poll_cq() call, there is no 
> system call involved ?
> 
> Right, for most devices poll_cq can be done just by looking 
> at memory in userspace without involving the kernel at all.
>