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:   Wed, 25 May 2022 08:12:34 +0000
From:   "Palczewski, Mateusz" <mateusz.palczewski@...el.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        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

>
>On Thu, May 12, 2022 at 10:55 AM Kai-Heng Feng <kai.heng.feng@...onical.com> wrote:
>>
>> 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.
>
>A gentle ping...
>
>Please let me know if this is a proper fix so I can send v2.
>
>Kai-Heng
>
Hi,
Looking good to me. Waiting for v2 version with fixes tag and then 
this will be fully accepted. 

Regards,
Mateusz 
>>
>> 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) {
>
>