netdev - Re: [RFC PATCH net-next 0/6] net/smc: Spread workload over multiple cores

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Date:   Thu, 27 Jan 2022 15:59:36 +0800
From:   Tony Lu <tonylu@...ux.alibaba.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, kgraul@...ux.ibm.com,
        kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org,
        RDMA mailing list <linux-rdma@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 0/6] net/smc: Spread workload over multiple
 cores

On Thu, Jan 27, 2022 at 08:21:07AM +0200, Leon Romanovsky wrote:
> On Thu, Jan 27, 2022 at 11:14:37AM +0800, Tony Lu wrote:
> > On Wed, Jan 26, 2022 at 11:28:06AM -0400, Jason Gunthorpe wrote:
> > > On Wed, Jan 26, 2022 at 03:23:22PM +0800, Tony Lu wrote:
> > > > On Sun, Jan 16, 2022 at 11:00:33AM +0200, Leon Romanovsky wrote:
> > > > > 
> > > > > Please CC RDMA mailing list next time.
> > > > > 
> > > > > Why didn't you use already existed APIs in drivers/infiniband/core/cq.c?
> > > > > ib_cq_pool_get() will do most if not all of your open-coded CQ spreading
> > > > > logic.
> > > > 
> > > > I am working on replacing with ib_cq_pool_get(), this need ib_poll_context
> > > > to indicate the poller which provides by ib_poll_handler(). It's okay
> > > > for now, but for the callback function. When it polled a ib_wc, it
> > > > would call wc->wr_cqe->done(cq, wc), which is the union with wr_id. The
> > > > wr_id is heavily used in SMC.
> > > 
> > > Part of using the new interface is converting to use wr_cqe, you
> > > should just do that work instead of trying to duplicate a core API in
> > > a driver.
> > 
> > Thanks for your advice. This patch set aims to improve performance with
> > current API in SMC protocol, which is more urgent. 
> 
> This code existed from 2017, it is hard to agree with "urgent" claim.

Yes, I agree with you that the code is old. I think there are two
problems, one for performance issue, the other one for API refactor.

We are running into the performance issues mentioned in patches in our
cloud environment. So I think it is more urgent for a real world issue.

The current modification is less intrusive to the code. This makes
changes simpler. And current implement works for now, this is why I put
refactor behind.

Thank you,
Tony Lu