On 2020/5/12 19:35, Leon Romanovsky wrote: > On Mon, May 11, 2020 at 01:54:48PM +0000, liweihang wrote: >> Hi All, >> >> I have two questions about masked atomic (Masked Compare and Swap & MFetchAdd): >> >> 1. The kernel now supports masked atomic, but the it does not support atomic >> operation. Is the masked atomic valid in kernel currently? > > Yes, it is valid, but probably has a very little real value for the kernel ULPs. > I see code in the RDS that uses atomics, but it says nothing to me, because > upstream RDS and version in-real-use are completely different. > >> 2. In the userspace, ofed does not have the corresponding opcode for the masked >> atomic (IB_WR_MASKED_ATOMIC_CMP_AND_SWP, IB_WR_MASKED_ATOMIC_FETCH_AND_ADD), >> and ibv_send_wr also has no related data segment for it. How to support it in >> userspace? > > ibv_send_wr is not extensible, so the real solution will need to extend ibv_wr_post() [1] > with specific and new post builders. > > Thanks > > [1] https://github.com/linux-rdma/rdma-core/blob/master/libibverbs/man/ibv_wr_post.3.md > Hi Leon, Thanks for your response. May I ask another question: Why it's not encouraged to use atomic/extended atomic/masked atomic operations in kernel? Jason said that there seems no kernel users of extended atomic, is there any other reasons? Weihang
