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From: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Date: Fri, 10 May 2024 16:37:08 -0400
To: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Cc: Andy Gospodarek <andrew.gospodarek@broadcom.com>,
	Ajit Khaparde <ajit.khaparde@broadcom.com>,
	Wei Huang <wei.huang2@amd.com>, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	netdev@vger.kernel.org, bhelgaas@google.com, corbet@lwn.net,
	davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, alex.williamson@redhat.com,
	michael.chan@broadcom.com, manoj.panicker2@amd.com,
	Eric.VanTassell@amd.com
Subject: Re: [PATCH V1 8/9] bnxt_en: Add TPH support in BNXT driver
Message-ID: <Zj6FdAb34o1-GNeV@C02YVCJELVCG.dhcp.broadcom.net>
References: <20240509162741.1937586-1-wei.huang2@amd.com>
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 <4c6a8b86-6544-4c99-a0f2-030e2ec4e98f@linux.dev>
 <Zj48BPYoFU1ISaiL@C02YVCJELVCG.dhcp.broadcom.net>
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On Fri, May 10, 2024 at 09:33:46PM +0100, Vadim Fedorenko wrote:
> On 10/05/2024 16:23, Andy Gospodarek wrote:
> > On Fri, May 10, 2024 at 11:35:35AM +0100, Vadim Fedorenko wrote:
> > > On 10.05.2024 04:55, Ajit Khaparde wrote:
> > > > On Thu, May 9, 2024 at 2:50 PM Vadim Fedorenko
> > > > <vadim.fedorenko@linux.dev> wrote:
> > > > > 
> > > > > On 09/05/2024 17:27, Wei Huang wrote:
> > > > > > From: Manoj Panicker <manoj.panicker2@amd.com>
> > > > > > 
> > > > > > As a usage example, this patch implements TPH support in Broadcom BNXT
> > > > > > device driver by invoking pcie_tph_set_st() function when interrupt
> > > > > > affinity is changed.
> > > > > > 
> > > > > > Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
> > > > > > Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
> > > > > > Reviewed-by: Wei Huang <wei.huang2@amd.com>
> > > > > > Signed-off-by: Manoj Panicker <manoj.panicker2@amd.com>
> > > > > > ---
> > > > > >     drivers/net/ethernet/broadcom/bnxt/bnxt.c | 51 +++++++++++++++++++++++
> > > > > >     drivers/net/ethernet/broadcom/bnxt/bnxt.h |  4 ++
> > > > > >     2 files changed, 55 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > > > > index 2c2ee79c4d77..be9c17566fb4 100644
> > > > > > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > > > > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > > > > > @@ -55,6 +55,7 @@
> > > > > >     #include <net/page_pool/helpers.h>
> > > > > >     #include <linux/align.h>
> > > > > >     #include <net/netdev_queues.h>
> > > > > > +#include <linux/pci-tph.h>
> > > > > > 
> > > > > >     #include "bnxt_hsi.h"
> > > > > >     #include "bnxt.h"
> > > > > > @@ -10491,6 +10492,7 @@ static void bnxt_free_irq(struct bnxt *bp)
> > > > > >                                 free_cpumask_var(irq->cpu_mask);
> > > > > >                                 irq->have_cpumask = 0;
> > > > > >                         }
> > > > > > +                     irq_set_affinity_notifier(irq->vector, NULL);
> > > > > >                         free_irq(irq->vector, bp->bnapi[i]);
> > > > > >                 }
> > > > > > 
> > > > > > @@ -10498,6 +10500,45 @@ static void bnxt_free_irq(struct bnxt *bp)
> > > > > >         }
> > > > > >     }
> > > > > > 
> > > > > > +static void bnxt_rtnl_lock_sp(struct bnxt *bp);
> > > > > > +static void bnxt_rtnl_unlock_sp(struct bnxt *bp);
> > > > > > +static void bnxt_irq_affinity_notify(struct irq_affinity_notify *notify,
> > > > > > +                                  const cpumask_t *mask)
> > > > > > +{
> > > > > > +     struct bnxt_irq *irq;
> > > > > > +
> > > > > > +     irq = container_of(notify, struct bnxt_irq, affinity_notify);
> > > > > > +     cpumask_copy(irq->cpu_mask, mask);
> > > > > > +
> > > > > > +     if (!pcie_tph_set_st(irq->bp->pdev, irq->msix_nr,
> > > > > > +                          cpumask_first(irq->cpu_mask),
> > > > > > +                          TPH_MEM_TYPE_VM, PCI_TPH_REQ_TPH_ONLY))
> > > > > > +             pr_err("error in configuring steering tag\n");
> > > > > > +
> > > > > > +     if (netif_running(irq->bp->dev)) {
> > > > > > +             rtnl_lock();
> > > > > > +             bnxt_close_nic(irq->bp, false, false);
> > > > > > +             bnxt_open_nic(irq->bp, false, false);
> > > > > > +             rtnl_unlock();
> > > > > > +     }
> > > > > 
> > > > > Is it really needed? It will cause link flap and pause in the traffic
> > > > > service for the device. Why the device needs full restart in this case?
> > > > 
> > > > In that sequence only the rings are recreated for the hardware to sync
> > > > up the tags.
> > > > 
> > > > Actually its not a full restart. There is no link reinit or other
> > > > heavy lifting in this sequence.
> > > > The pause in traffic may be momentary. Do IRQ/CPU affinities change frequently?
> > > > Probably not?
> > > 
> > >  From what I can see in bnxt_en, proper validation of link_re_init parameter is
> > > not (yet?) implemented, __bnxt_open_nic will unconditionally call
> > > netif_carrier_off() which will be treated as loss of carrier with counters
> > > increment and proper events posted. Changes to CPU affinities were
> > > non-disruptive before the patch, but now it may break user-space
> > > assumptions.
> > 
> >  From my testing the link should not flap.  I just fired up a recent net-next
> > and confirmed the same by calling $ ethtool -G ens7f0np0 rx 1024 which does a
> > similar bnxt_close_nic(bp, false, false)/bnxt_open_nic(bp, false, false) as
> > this patch.  Link remained up -- even with a non-Broadocm link-partner.
> 
> Hi Andy!
> 
> Well, it might be that from phy PoV the link didn't flap, but from network
> subsystem it does flap:
> 
> [root@host ~]# ethtool -G eth0 rx 512
> [root@host ~]# cat /sys/class/net/eth0/carrier_changes
> 6
> [root@host ~]# ethtool -G eth0 rx 1024
> [root@host ~]# cat /sys/class/net/eth0/carrier_changes
> 8

Fair point :)

I also think that we should skip doing the bnxt_close_nic/bnxt_open_nic
except when TPH is possible on the system.  That should mitigate some of
these concerns for users who do not have it enabled.

> And this is what I'm referring to when talking about user-space experience.
> But I would like to see new ndo_queue_stop/start implementation, it may help
> in this situation.
> 
> > > Does FW need full rings re-init to update target value, which is one u32 write?
> > > It looks like overkill TBH.
> > 
> > Full rings do not, but the initialization of that particular ring associated
> > with this irq does need to be done.  On my list of things we need to do in
> > bnxt_en is implement the new ndo_queue_stop/start and ndo_queue_mem_alloc/free
> > operations and once those are done we could make a switch as that may be less
> > disruptive.
> > 
> > > And yes, affinities can be change on fly according to the changes of the
> > > workload on the host.
> > > 
> > > > > 
> > > > > 
> > > > > > +}
> > > > > > +
> > > > > > +static void bnxt_irq_affinity_release(struct kref __always_unused *ref)
> > > > > > +{
> > > > > > +}
> > > > > > +
> > > > > > +static inline void __bnxt_register_notify_irqchanges(struct bnxt_irq *irq)
> > > > > 
> > > > > No inlines in .c files, please. Let compiler decide what to inline.
> > > > > 
> > > > > > +{
> > > > > > +     struct irq_affinity_notify *notify;
> > > > > > +
> > > > > > +     notify = &irq->affinity_notify;
> > > > > > +     notify->irq = irq->vector;
> > > > > > +     notify->notify = bnxt_irq_affinity_notify;
> > > > > > +     notify->release = bnxt_irq_affinity_release;
> > > > > > +
> > > > > > +     irq_set_affinity_notifier(irq->vector, notify);
> > > > > > +}
> > > > > > +
> > > > > >     static int bnxt_request_irq(struct bnxt *bp)
> > > > > >     {
> > > > > >         int i, j, rc = 0;
> > > > > > @@ -10543,6 +10584,7 @@ static int bnxt_request_irq(struct bnxt *bp)
> > > > > >                         int numa_node = dev_to_node(&bp->pdev->dev);
> > > > > > 
> > > > > >                         irq->have_cpumask = 1;
> > > > > > +                     irq->msix_nr = map_idx;
> > > > > >                         cpumask_set_cpu(cpumask_local_spread(i, numa_node),
> > > > > >                                         irq->cpu_mask);
> > > > > >                         rc = irq_set_affinity_hint(irq->vector, irq->cpu_mask);
> > > > > > @@ -10552,6 +10594,15 @@ static int bnxt_request_irq(struct bnxt *bp)
> > > > > >                                             irq->vector);
> > > > > >                                 break;
> > > > > >                         }
> > > > > > +
> > > > > > +                     if (!pcie_tph_set_st(bp->pdev, i,
> > > > > > +                                          cpumask_first(irq->cpu_mask),
> > > > > > +                                          TPH_MEM_TYPE_VM, PCI_TPH_REQ_TPH_ONLY)) {
> > > > > > +                             netdev_err(bp->dev, "error in setting steering tag\n");
> > > > > > +                     } else {
> > > > > > +                             irq->bp = bp;
> > > > > > +                             __bnxt_register_notify_irqchanges(irq);
> > > > > > +                     }
> > > > > >                 }
> > > > > >         }
> > > > > >         return rc;
> > > > > > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.h b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> > > > > > index dd849e715c9b..0d3442590bb4 100644
> > > > > > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> > > > > > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> > > > > > @@ -1195,6 +1195,10 @@ struct bnxt_irq {
> > > > > >         u8              have_cpumask:1;
> > > > > >         char            name[IFNAMSIZ + 2];
> > > > > >         cpumask_var_t   cpu_mask;
> > > > > > +
> > > > > > +     int             msix_nr;
> > > > > > +     struct bnxt     *bp;
> > > > > > +     struct irq_affinity_notify affinity_notify;
> > > > > >     };
> > > > > > 
> > > > > >     #define HWRM_RING_ALLOC_TX  0x1
> > > > > 
> > > 
>