Re: [PATCH 2/2] RDMA/nes: add support of iWARP multicast acceleration over IB_QPT_RAW_ETY QP type

[Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

Walukiewicz, Miroslaw wrote:
> Hello Steve,
>
> Our Hw QP is not a UD type QP but L2 raw QP. In verbs API there is assumtion that user provides a data payload only for TX and similarly receives a payload only. The protocol headers (in case of UD - MAC/IP/UDP) are attached by HW. 
>
> Our QP implementation in HW  does not provide such possibity of attaching headers by HW for UD traffic so for multicast acceleration we choose L2 raw path. It provides some overhead for user application but it is still zero copy apprach.
>
> I thought about using a simulation of UD path using L2 raw QP to get the same result like for true UD QP (user handles a payload only). Such approach costs additional copy of payload in SW due to putting headers first and next payload to single tx buffer. Similar situation is for rx. It is a need for copy payload to posted buffers or provide data with some offset. 
>
> ud_post_send and friends implements the transmit path for IMA. Our RAW ETH QP needs access to physical addresses from user space. Due to security reasons we should make a virtual-to-physical address translation in kernel. 
>
>   

But why couldn't you just use the normal memory registration paths?  IE 
the user mode app does ibv_reg_mr() and then uses lkey/addr/len in SGEs 
in the ibv_post_send() which could do kernel bypass.

> Unfortunately an OFED path for ibv_post_send diving to kernel is quite slow due to some number of dynamic memory allocations in the path. We choose to create own private post_send channel to increase tx bandwidth using ud_post_send and friends.

Seems like maybe you could fix the non-bypass post_send/recv paths 
instead of implementing an entirely new user<->kernel interface...

Steve.


>  
>
> Regards,
>
> Mirek
>
> -----Original Message-----
> From: Steve Wise [mailto:swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org] 
> Sent: Tuesday, May 04, 2010 7:19 PM
> To: Walukiewicz, Miroslaw
> Cc: rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Subject: Re: [PATCH 2/2] RDMA/nes: add support of iWARP multicast acceleration over IB_QPT_RAW_ETY QP type
>
> Hey Mirek,
>
> It looks like this patch adds a new file interface for a UD service.  
> Why didn't you extend the existing UD interface as needed? 
>
> What IO is supported with these changes?  IMA via the raw QP, but what 
> ud_post_send() and friends used for?
>
>
> Steve.
>
>
>
> miroslaw.walukiewicz-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org wrote:
>   
>> This patch implements iWarp multicast acceleration (IMA)
>> over IB_QPT_RAW_ETY QP type in nes driver.
>>
>> Application creates a raw eth QP (IBV_QPT_RAW_ETH in user-space) and
>> manages the multicast via ibv_attach_mcast and ibv_detach_mcast calls.
>>
>> Calling ibv_attach_mcast/ibv_datach_mcast has an effect of
>> enabling/disabling L2 MAC address filters in HW.
>>
>> Signed-off-by: Mirek Walukiewicz <miroslaw.walukiewicz-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>>
>>
>>
>>     

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