Re: {RFC] ibv_post_send()/ibv_post_recv() kernel path optimizations

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > The proposed path optimization is removing of dynamic allocations 
 > by redefining a structure definition passed to kernel. 

 > To 
 > 
 > struct ibv_post_send {
 >         __u32 command;
 >         __u16 in_words;
 >         __u16 out_words;
 >         __u64 response;
 >         __u32 qp_handle;
 >         __u32 wr_count;
 >         __u32 sge_count;
 >         __u32 wqe_size;
 >         struct ibv_kern_send_wr send_wr[512];
 > };

I don't see how this can possibly work.  Where does the scatter/gather
list go if you make this have a fixed size array of send_wr?

Also I don't see why you need to change the user/kernel ABI at all to
get rid of dynamic allocations... can't you just have the kernel keep a
cached send_wr allocation (say, per user context) and reuse that?  (ie
allocate memory but don't free the first time into post_send, and only
reallocate if a bigger send request comes, and only free when destroying
the context)

 - R.
-- 
Roland Dreier <rolandd-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> || For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/index.html
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