From: Jakub Kicinski <kuba@kernel.org>
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Haiyang Zhang <haiyangz@linux.microsoft.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
KY Srinivasan <kys@microsoft.com>, Wei Liu <wei.liu@kernel.org>,
Dexuan Cui <DECUI@microsoft.com>, Long Li <longli@microsoft.com>,
Andrew Lunn <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
Konstantin Taranov <kotaranov@microsoft.com>,
Simon Horman <horms@kernel.org>,
Erni Sri Satya Vennela <ernis@linux.microsoft.com>,
Shradha Gupta <shradhagupta@linux.microsoft.com>,
Saurabh Sengar <ssengar@linux.microsoft.com>,
Aditya Garg <gargaditya@linux.microsoft.com>,
Dipayaan Roy <dipayanroy@linux.microsoft.com>,
Shiraz Saleem <shirazsaleem@microsoft.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
Paul Rosswurm <paulros@microsoft.com>
Subject: Re: [EXTERNAL] Re: [PATCH V2,net-next, 1/2] net: mana: Add support for coalesced RX packets on CQE
Date: Tue, 13 Jan 2026 17:09:48 -0800 [thread overview]
Message-ID: <20260113170948.1d6fbdaf@kernel.org> (raw)
In-Reply-To: <SA3PR21MB3867A54AA709CEE59F610943CA8EA@SA3PR21MB3867.namprd21.prod.outlook.com>
On Tue, 13 Jan 2026 15:13:24 +0000 Haiyang Zhang wrote:
> > > I get that. What is the logic for combining 4 packets into a single
> > > completion? How does it work? Your commit message mentions "regression
> > > on latency" - what is the bound on that regression?
> >
> > When we received CQE type CQE_RX_COALESCED_4, it's a coalesced CQE. And in
> > the CQE OOB, there is an array with 4 PPI elements, with each pkt's length:
> > oob->ppi[i].pkt_len.
> >
> > So we read the related WQE and the DMA buffers for the RX pkt payloads, up
> > to 4.
> > But, if the coalesced pkts <4, the pkt_len will be 0 after the last pkt,
> > so we know when to stop reading the WQEs.
>
> And, the coalescing can add up to 2 microseconds into one-way latency.
I am asking you how the _device_ (hypervisor?) decides when to coalesce
and when to send a partial CQE (<4 packets in 4 pkt CQE). You are using
the coalescing uAPI, so I'm trying to make sure this is the correct API.
CQE configuration can also be done via ringparam.
next prev parent reply other threads:[~2026-01-14 1:09 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-06 20:46 [PATCH V2,net-next, 0/2] net: mana: Add support for coalesced RX packets Haiyang Zhang
2026-01-06 20:46 ` [PATCH V2,net-next, 1/2] net: mana: Add support for coalesced RX packets on CQE Haiyang Zhang
2026-01-06 21:50 ` Long Li
2026-01-10 1:56 ` Jakub Kicinski
2026-01-12 21:01 ` [EXTERNAL] " Haiyang Zhang
2026-01-13 1:21 ` Jakub Kicinski
2026-01-13 15:09 ` Haiyang Zhang
2026-01-13 15:13 ` Haiyang Zhang
2026-01-14 1:09 ` Jakub Kicinski [this message]
2026-01-14 18:27 ` Haiyang Zhang
2026-01-15 2:54 ` Jakub Kicinski
2026-01-15 19:57 ` Haiyang Zhang
2026-01-16 2:14 ` Jakub Kicinski
2026-01-16 16:44 ` Haiyang Zhang
2026-01-17 16:58 ` Jakub Kicinski
2026-01-17 18:01 ` Haiyang Zhang
2026-01-17 22:48 ` Jakub Kicinski
2026-01-18 18:31 ` Haiyang Zhang
2026-02-22 21:32 ` Haiyang Zhang
2026-01-06 20:46 ` [PATCH V2,net-next, 2/2] net: mana: Add ethtool counters for RX CQEs in coalesced type Haiyang Zhang
2026-01-06 22:10 ` Long Li
2026-01-10 1:56 ` Jakub Kicinski
2026-01-12 21:03 ` [EXTERNAL] " Haiyang Zhang
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