linux-kernel - RE: [PATCH v2] net: mana: Batch ringing RX queue doorbell on receiving packets

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Message-ID: <PH7PR21MB3263595D72A3C2EC871D668CCE26A@PH7PR21MB3263.namprd21.prod.outlook.com>
Date:   Mon, 26 Jun 2023 22:55:24 +0000
From:   Long Li <longli@...rosoft.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>
CC:     Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
        Ajay Sharma <sharmaajay@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2] net: mana: Batch ringing RX queue doorbell on
 receiving packets

> Subject: Re: [PATCH v2] net: mana: Batch ringing RX queue doorbell on
> receiving packets
> 
> On Thu, 22 Jun 2023 09:22:36 -0700 longli@...uxonhyperv.com wrote:
> > It's inefficient to ring the doorbell page every time a WQE is posted
> > to the received queue.
> >
> > Move the code for ringing doorbell page to where after we have posted
> > all WQEs to the receive queue during a callback from napi_poll().
> >
> > Tests showed no regression in network latency benchmarks.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: ca9c54d2d6a5 ("net: mana: Add a driver for Microsoft Azure
> > Network Adapter (MANA)")
> 
> If this is supposed to be a fix, you need to clearly explain what the
> performance loss was, so that backporters can make an informed decision.

I'm sending v3 to include the details.

> 
> >  drivers/net/ethernet/microsoft/mana/gdma_main.c |  5 ++++-
> >  drivers/net/ethernet/microsoft/mana/mana_en.c   | 10 ++++++++--
> >  2 files changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > index 8f3f78b68592..ef11d09a3655 100644
> > --- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > +++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
> > @@ -300,8 +300,11 @@ static void mana_gd_ring_doorbell(struct
> > gdma_context *gc, u32 db_index,
> >
> >  void mana_gd_wq_ring_doorbell(struct gdma_context *gc, struct
> > gdma_queue *queue)  {
> > +	/* BNIC Spec specifies that client should set 0 for rq.wqe_cnt
> > +	 * This value is not used in sq
> > +	 */
> >  	mana_gd_ring_doorbell(gc, queue->gdma_dev->doorbell, queue-
> >type,
> > -			      queue->id, queue->head * GDMA_WQE_BU_SIZE,
> 1);
> > +			      queue->id, queue->head * GDMA_WQE_BU_SIZE,
> 0);
> >  }
> 
> This change needs to be explained in the commit message, or should be a
> separate patch.

Will explain the change in the commit message.

Thanks,
Long

> --
> pw-bot: cr