[J/Unstable/OEM-5.14/OEM-5.17] [PATCH 1/1] UBUNTU: SAUCE: igb: Make DMA faster when CPU is active on the PCIe link

[Kai-Heng Feng]

On Wed, Jun 1, 2022 at 10:16 PM Tim Gardner <tim.gardner at canonical.com> wrote:
>
> How about we wait until this gets merged upstream before applying it to
> a 22.04 kernel that we have to maintain for the next 10 years ? The
> fewer SAUCE patches, the better.

Yea I guess we can skip Jammy for now. Upstream stable will probably
pick this up automatically anyway.

>
> Your bug report also does not state what the current performance is, so
> its hard to tell if the gains are worth the extra code maintenance.

Without the fix the iperf speed is around 700Mbps.

Kai-Heng

>
> rtg
>
> On 5/31/22 20:29, Kai-Heng Feng wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1976438
> >
> > Intel I210 on some Intel Alder Lake platforms can only achieve ~750Mbps
> > Tx speed via iperf. The RR2DCDELAY shows around 0x2xxx DMA delay, which
> > will be 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.
> >
> > Fixes: b6e0c419f040 ("igb: Move DMA Coalescing init code to separate function.")
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
> > (cherry picked from commit 071ab8cbab26883af46b6ff1eb70616938350275 git://git.kernel.org/pub/scm/linux/kernel/git/tnguy/next-queue.git dev-queue)
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.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 68be2976f539f..c0d93fd19c1ed 100644
> > --- a/drivers/net/ethernet/intel/igb/igb_main.c
> > +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> > @@ -9898,11 +9898,10 @@ 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);
> >
> > @@ -9935,7 +9934,6 @@ 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
> > @@ -9952,12 +9950,12 @@ 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) {
>
> --
> -----------
> Tim Gardner
> Canonical, Inc