linux-kernel - RE: [PATCH V3,net-next] net: mana: Add page pool for RX buffers

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Message-ID: <PH7PR21MB3116F5612AA8303512EEBA4CCA03A@PH7PR21MB3116.namprd21.prod.outlook.com>
Date:   Tue, 25 Jul 2023 19:02:10 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "brouer@...hat.com" <brouer@...hat.com>,
        Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Paul Rosswurm <paulros@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "leon@...nel.org" <leon@...nel.org>,
        Long Li <longli@...rosoft.com>,
        "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        Ajay Sharma <sharmaajay@...rosoft.com>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "shradhagupta@...ux.microsoft.com" <shradhagupta@...ux.microsoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: RE: [PATCH V3,net-next] net: mana: Add page pool for RX buffers



> -----Original Message-----
> From: Jesper Dangaard Brouer <jbrouer@...hat.com>
> Sent: Tuesday, July 25, 2023 2:01 PM
> >>
> >> Our driver is using NUMA 0 by default, so I implicitly assign NUMA node id
> >> to zero during pool init.
> >>
> >> And, if the IRQ/CPU affinity is changed, the page_pool_nid_changed()
> >> will update the nid for the pool. Does this sound good?
> >>
> >
> > Also, since our driver is getting the default node from here:
> > 	gc->numa_node = dev_to_node(&pdev->dev);
> > I will update this patch to set the default node as above, instead of implicitly
> > assigning it to 0.
> >
> 
> In that case, I agree that it make sense to use dev_to_node(&pdev->dev),
> like:
> 	pprm.nid = dev_to_node(&pdev->dev);
> 
> Driver must have a reason for assigning gc->numa_node for this hardware,
> which is okay. That is why page_pool API allows driver to control this.
> 
> But then I don't think you should call page_pool_nid_changed() like
> 
> 	page_pool_nid_changed(rxq->page_pool, numa_mem_id());
> 
> Because then you will (at first packet processing event) revert the
> dev_to_node() setting to use numa_mem_id() of processing/running CPU.
> (In effect this will be the same as setting NUMA_NO_NODE).
> 
> I know, mlx5 do call page_pool_nid_changed(), but they showed benchmark
> numbers that this was preferred action, even-when sysadm had
> "misconfigured" the default smp_affinity RX-processing to happen on a
> remote NUMA node.  AFAIK mlx5 keeps the descriptor rings on the
> originally configured NUMA node that corresponds to the NIC PCIe slot.

In mana_gd_setup_irqs(), we set the default IRQ/CPU affinity to gc->numa_node 
too, so it won't revert the nid initial setting. 

Currently, the Azure hypervisor always indicates numa 0 as default. (In 
the future, it will start to provide the accurate default dev node.) When a 
user manually changes the IRQ/CPU affinity for perf tuning, we want to 
allow page_pool_nid_changed() to update the pool. Is this OK?

Thanks,
- Haiyang