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Message-ID: <PH7PR21MB3263B266E381BA15DCE45820CE25A@PH7PR21MB3263.namprd21.prod.outlook.com>
Date: Thu, 29 Jun 2023 18:18:37 +0000
From: Long Li <longli@...rosoft.com>
To: Paolo Abeni <pabeni@...hat.com>,
"longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
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>,
Jakub Kicinski <kuba@...nel.org>
CC: "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 v3] net: mana: Batch ringing RX queue doorbell on
receiving packets
> Subject: Re: [Patch v3] net: mana: Batch ringing RX queue doorbell on receiving
> packets
>
> On Mon, 2023-06-26 at 16:57 -0700, longli@...uxonhyperv.com wrote:
> > From: Long Li <longli@...rosoft.com>
> >
> > It's inefficient to ring the doorbell page every time a WQE is posted
> > to the received queue. Excessive MMIO writes result in CPU spending
> > more time waiting on LOCK instructions (atomic operations), resulting
> > in poor scaling performance.
> >
> > 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().
> >
> > With this change, tests showed an improvement from 120G/s to 160G/s on
> > a 200G physical link, with 16 or 32 hardware queues.
> >
> > Tests showed no regression in network latency benchmarks on single
> > connection.
> >
> > While we are making changes in this code path, change the code for
> > ringing doorbell to set the WQE_COUNT to 0 for Receive Queue. The
> > hardware specification specifies that it should set to 0. Although
> > currently the hardware doesn't enforce the check, in the future
> > releases it may do.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: ca9c54d2d6a5 ("net: mana: Add a driver for Microsoft Azure
> > Network Adapter (MANA)")
>
> Uhmmm... this looks like a performance improvement to me, more suitable for
> the net-next tree ?!? (Note that net-next is closed now).
This issue is a blocker for usage on 200G physical link. I think it can be categorized as a fix.
>
> In any case you must avoid empty lines in the tag area.
>
> If you really intend targeting the -net tree, please repost fixing the above and
> explicitly specifying the target tree in the subj prefix.
Will do, thank you.
Long
>
> thanks!
>
> Paolo
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