netdev - Re: [Intel-wired-lan] [PATCH 2/2] igb: Make DMA faster when CPU is active on the PCIe link

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Date:   Thu, 12 May 2022 10:55:50 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        intel-wired-lan@...ts.osuosl.org, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH 2/2] igb: Make DMA faster when CPU is
 active on the PCIe link

Hi Paul,

On Wed, May 11, 2022 at 8:49 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
>
> Dear Kai-Hang,
>
>
> Thank you for the patch.
>
>
> Am 11.05.22 um 14:28 schrieb Kai-Heng Feng:
> > We found Intel I210 can only achieve ~750Mbps Tx speed on some
> > platforms. The RR2DCDELAY shows around 0x2xxx DMA delay, which will be
>
> Please give an example platform, where it works and where it does not.

The platform is about but not yet hit the market yet, so I can't disclose it.
They are Intel Alder Lake based.

>
> How did you test transfer speed?

Iperf.

>
> > significantly lower when 1) ASPM is disabled or 2) SoC package c-state
> > stays above PC3. When the RR2DCDELAY is around 0x1xxx the Tx speed can
> > reach to ~950Mbps.
> >
> > According to the I210 datasheet "8.26.1 PCIe Misc. Register - PCIEMISC",
> > "DMA Idle Indication" doesn't seem to tie to DMA coalesce anymore, so
> > set it to 1b for "DMA is considered idle when there is no Rx or Tx AND
> > when there are no TLPs indicating that CPU is active detected on the
> > PCIe link (such as the host executes CSR or Configuration register read
> > or write operation)" and performing Tx should also fall under "active
> > CPU on PCIe link" case.
> >
> > In addition to that, commit b6e0c419f040 ("igb: Move DMA Coalescing init
> > code to separate function.") seems to wrongly changed from enabling
> > E1000_PCIEMISC_LX_DECISION to disabling it, also fix that.
>
> Please split this into a separate commit with Fixes tag, and maybe the
> commit author in Cc.

I don't see the need to split to separate commit as both require the
same change.

I will add the "Fixes" tag once the igb maintainers reviewed the patch.

Kai-Heng

>
>
> Kind regards,
>
> Paul
>
>
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > ---
> >   drivers/net/ethernet/intel/igb/igb_main.c | 12 +++++-------
> >   1 file changed, 5 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> > index 34b33b21e0dcd..eca797dded429 100644
> > --- a/drivers/net/ethernet/intel/igb/igb_main.c
> > +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> > @@ -9897,11 +9897,10 @@ static void igb_init_dmac(struct igb_adapter *adapter, u32 pba)
> >       struct e1000_hw *hw = &adapter->hw;
> >       u32 dmac_thr;
> >       u16 hwm;
> > +     u32 reg;
> >
> >       if (hw->mac.type > e1000_82580) {
> >               if (adapter->flags & IGB_FLAG_DMAC) {
> > -                     u32 reg;
> > -
> >                       /* force threshold to 0. */
> >                       wr32(E1000_DMCTXTH, 0);
> >
> > @@ -9934,7 +9933,6 @@ static void igb_init_dmac(struct igb_adapter *adapter, u32 pba)
> >                       /* Disable BMC-to-OS Watchdog Enable */
> >                       if (hw->mac.type != e1000_i354)
> >                               reg &= ~E1000_DMACR_DC_BMC2OSW_EN;
> > -
> >                       wr32(E1000_DMACR, reg);
> >
> >                       /* no lower threshold to disable
> > @@ -9951,12 +9949,12 @@ static void igb_init_dmac(struct igb_adapter *adapter, u32 pba)
> >                        */
> >                       wr32(E1000_DMCTXTH, (IGB_MIN_TXPBSIZE -
> >                            (IGB_TX_BUF_4096 + adapter->max_frame_size)) >> 6);
> > +             }
> >
> > -                     /* make low power state decision controlled
> > -                      * by DMA coal
> > -                      */
> > +             if (hw->mac.type >= e1000_i210 ||
> > +                 (adapter->flags & IGB_FLAG_DMAC)) {
> >                       reg = rd32(E1000_PCIEMISC);
> > -                     reg &= ~E1000_PCIEMISC_LX_DECISION;
> > +                     reg |= E1000_PCIEMISC_LX_DECISION;
> >                       wr32(E1000_PCIEMISC, reg);
> >               } /* endif adapter->dmac is not disabled */
> >       } else if (hw->mac.type == e1000_82580) {