netdev - Re: [PATCH v2 2/3] net: mhi: Get RX queue size from MHI core

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Date:   Fri, 11 Dec 2020 15:45:10 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Loic Poulain <loic.poulain@...aro.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>
Subject: Re: [PATCH v2 2/3] net: mhi: Get RX queue size from MHI core

On Fri, Dec 11, 2020 at 10:40:13AM +0100, Loic Poulain wrote:
> Hi Mani,
> 
> On Fri, 11 Dec 2020 at 06:38, Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> >
> > On Thu, Dec 10, 2020 at 12:15:50PM +0100, Loic Poulain wrote:
> > > The RX queue size can be determined at runtime by retrieving the
> > > number of available transfer descriptors.
> > >
> > > Signed-off-by: Loic Poulain <loic.poulain@...aro.org>
> > > ---
> > >  v2: Fixed commit message typo
> > >
> > >  drivers/net/mhi_net.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> [...]
> > > -
> > >       INIT_DELAYED_WORK(&mhi_netdev->rx_refill, mhi_net_rx_refill_work);
> > >       u64_stats_init(&mhi_netdev->stats.rx_syncp);
> > >       u64_stats_init(&mhi_netdev->stats.tx_syncp);
> > > @@ -268,6 +265,9 @@ static int mhi_net_probe(struct mhi_device *mhi_dev,
> > >       if (err)
> > >               goto out_err;
> > >
> > > +     /* Number of transfer descriptors determines size of the queue */
> > > +     mhi_netdev->rx_queue_sz = mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE);
> > > +
> >
> > This value is not static right? You might need to fetch the count in
> > mhi_net_rx_refill_work().
> 
> It is, actually here driver is just looking for the total queue size,
> which is the number of descriptors at init time. This total queue size
> is used later to determine the level of MHI queue occupancy rate.
> 

Right but what if the size got increased in runtime (recycled etc...), we won't
be fully utilizing the ring.

Thanks,
Mani

> Regards,
> Loic