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Date: Sat, 18 Apr 2020 15:39:17 -0700
From: Chris Healy <cphealy@...il.com>
To: Andy Duan <fugang.duan@....com>
Cc: Andrew Lunn <andrew@...n.ch>, David Miller <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
Florian Fainelli <f.fainelli@...il.com>,
Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [EXT] [PATCH net-next v2 1/3] net: ethernet: fec: Replace
interrupt driven MDIO with polled IO
I did some profiling using an oscilloscope with my NXP Vybrid based
platform to see what different "sleep_us" values resulted in for start
of MDIO to start of MDIO transaction times. Here's what I found:
0 - ~38us to ~40us
1 - ~48us to ~64us
2 - ~48us to ~64us
3 - ~48us to ~64us
4 - ~48us to ~64us
4 - ~48us to ~64us
5 - ~48us to ~64us
6 - ~48us to ~64us
7 - ~48us to ~64us
8 - ~48us to ~64us
9 - ~56us to ~88us
10 - ~56us to ~112us
Basically, with the "sleep_us" value set to 0, I would get the
shortest inter transaction times with a very low variance. Once I
went to a non-zero value, the inter transaction time went up, as well
as the variance, which I suppose makes sense....
On Sat, Apr 18, 2020 at 6:55 AM Andy Duan <fugang.duan@....com> wrote:
>
> From: Andrew Lunn <andrew@...n.ch> Sent: Saturday, April 18, 2020 8:04 AM
> > Measurements of the MDIO bus have shown that driving the MDIO bus using
> > interrupts is slow. Back to back MDIO transactions take about 90uS, with
> > 25uS spent performing the transaction, and the remainder of the time the bus
> > is idle.
> >
> > Replacing the completion interrupt with polled IO results in back to back
> > transactions of 40uS. The polling loop waiting for the hardware to complete
> > the transaction takes around 27uS. Which suggests interrupt handling has an
> > overhead of 50uS, and polled IO nearly halves this overhead, and doubles the
> > MDIO performance.
> >
> > Suggested-by: Chris Heally <cphealy@...il.com>
> > Signed-off-by: Andrew Lunn <andrew@...n.ch>
> > ---
> > drivers/net/ethernet/freescale/fec.h | 4 +-
> > drivers/net/ethernet/freescale/fec_main.c | 67 ++++++++++++-----------
> > 2 files changed, 35 insertions(+), 36 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/fec.h
> > b/drivers/net/ethernet/freescale/fec.h
> > index e74dd1f86bba..a6cdd5b61921 100644
> > --- a/drivers/net/ethernet/freescale/fec.h
> > +++ b/drivers/net/ethernet/freescale/fec.h
> > @@ -376,8 +376,7 @@ struct bufdesc_ex {
> > #define FEC_ENET_TS_AVAIL ((uint)0x00010000)
> > #define FEC_ENET_TS_TIMER ((uint)0x00008000)
> >
> > -#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF |
> > FEC_ENET_MII) -#define FEC_NAPI_IMASK FEC_ENET_MII
> > +#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF)
> > #define FEC_RX_DISABLED_IMASK (FEC_DEFAULT_IMASK &
> > (~FEC_ENET_RXF))
> >
> > /* ENET interrupt coalescing macro define */ @@ -543,7 +542,6 @@ struct
> > fec_enet_private {
> > int link;
> > int full_duplex;
> > int speed;
> > - struct completion mdio_done;
> > int irq[FEC_IRQ_NUM];
> > bool bufdesc_ex;
> > int pause_flag;
> > diff --git a/drivers/net/ethernet/freescale/fec_main.c
> > b/drivers/net/ethernet/freescale/fec_main.c
> > index dc6f8763a5d4..6530829632b1 100644
> > --- a/drivers/net/ethernet/freescale/fec_main.c
> > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > @@ -976,8 +976,8 @@ fec_restart(struct net_device *ndev)
> > writel((__force u32)cpu_to_be32(temp_mac[1]),
> > fep->hwp + FEC_ADDR_HIGH);
> >
> > - /* Clear any outstanding interrupt. */
> > - writel(0xffffffff, fep->hwp + FEC_IEVENT);
> > + /* Clear any outstanding interrupt, except MDIO. */
> > + writel((0xffffffff & ~FEC_ENET_MII), fep->hwp + FEC_IEVENT);
> >
> > fec_enet_bd_init(ndev);
> >
> > @@ -1123,7 +1123,7 @@ fec_restart(struct net_device *ndev)
> > if (fep->link)
> > writel(FEC_DEFAULT_IMASK, fep->hwp + FEC_IMASK);
> > else
> > - writel(FEC_ENET_MII, fep->hwp + FEC_IMASK);
> > + writel(0, fep->hwp + FEC_IMASK);
> >
> > /* Init the interrupt coalescing */
> > fec_enet_itr_coal_init(ndev);
> > @@ -1652,6 +1652,10 @@ fec_enet_interrupt(int irq, void *dev_id)
> > irqreturn_t ret = IRQ_NONE;
> >
> > int_events = readl(fep->hwp + FEC_IEVENT);
> > +
> > + /* Don't clear MDIO events, we poll for those */
> > + int_events &= ~FEC_ENET_MII;
> > +
> > writel(int_events, fep->hwp + FEC_IEVENT);
> > fec_enet_collect_events(fep, int_events);
> >
> > @@ -1659,16 +1663,12 @@ fec_enet_interrupt(int irq, void *dev_id)
> > ret = IRQ_HANDLED;
> >
> > if (napi_schedule_prep(&fep->napi)) {
> > - /* Disable the NAPI interrupts */
> > - writel(FEC_NAPI_IMASK, fep->hwp +
> > FEC_IMASK);
> > + /* Disable interrupts */
> > + writel(0, fep->hwp + FEC_IMASK);
> > __napi_schedule(&fep->napi);
> > }
> > }
> >
> > - if (int_events & FEC_ENET_MII) {
> > - ret = IRQ_HANDLED;
> > - complete(&fep->mdio_done);
> > - }
> > return ret;
> > }
> >
> > @@ -1818,11 +1818,24 @@ static void fec_enet_adjust_link(struct
> > net_device *ndev)
> > phy_print_status(phy_dev); }
> >
> > +static int fec_enet_mdio_wait(struct fec_enet_private *fep) {
> > + uint ievent;
> > + int ret;
> > +
> > + ret = readl_poll_timeout(fep->hwp + FEC_IEVENT, ievent,
> > + ievent & FEC_ENET_MII, 0, 30000);
>
> sleep X us between reads ?
>
> > +
> > + if (!ret)
> > + writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);
> > +
> > + return ret;
> > +}
> > +
> > static int fec_enet_mdio_read(struct mii_bus *bus, int mii_id, int regnum) {
> > struct fec_enet_private *fep = bus->priv;
> > struct device *dev = &fep->pdev->dev;
> > - unsigned long time_left;
> > int ret = 0, frame_start, frame_addr, frame_op;
> > bool is_c45 = !!(regnum & MII_ADDR_C45);
> >
> > @@ -1830,8 +1843,6 @@ static int fec_enet_mdio_read(struct mii_bus *bus,
> > int mii_id, int regnum)
> > if (ret < 0)
> > return ret;
> >
> > - reinit_completion(&fep->mdio_done);
> > -
> > if (is_c45) {
> > frame_start = FEC_MMFR_ST_C45;
> >
> > @@ -1843,11 +1854,9 @@ static int fec_enet_mdio_read(struct mii_bus
> > *bus, int mii_id, int regnum)
> > fep->hwp + FEC_MII_DATA);
> >
> > /* wait for end of transfer */
> > - time_left =
> > wait_for_completion_timeout(&fep->mdio_done,
> > - usecs_to_jiffies(FEC_MII_TIMEOUT));
> > - if (time_left == 0) {
> > + ret = fec_enet_mdio_wait(fep);
> > + if (ret) {
> > netdev_err(fep->netdev, "MDIO address write
> > timeout\n");
> > - ret = -ETIMEDOUT;
> > goto out;
> > }
> >
> > @@ -1866,11 +1875,9 @@ static int fec_enet_mdio_read(struct mii_bus
> > *bus, int mii_id, int regnum)
> > FEC_MMFR_TA, fep->hwp + FEC_MII_DATA);
> >
> > /* wait for end of transfer */
> > - time_left = wait_for_completion_timeout(&fep->mdio_done,
> > - usecs_to_jiffies(FEC_MII_TIMEOUT));
> > - if (time_left == 0) {
> > + ret = fec_enet_mdio_wait(fep);
> > + if (ret) {
> > netdev_err(fep->netdev, "MDIO read timeout\n");
> > - ret = -ETIMEDOUT;
> > goto out;
> > }
> >
> > @@ -1888,7 +1895,6 @@ static int fec_enet_mdio_write(struct mii_bus *bus,
> > int mii_id, int regnum, {
> > struct fec_enet_private *fep = bus->priv;
> > struct device *dev = &fep->pdev->dev;
> > - unsigned long time_left;
> > int ret, frame_start, frame_addr;
> > bool is_c45 = !!(regnum & MII_ADDR_C45);
> >
> > @@ -1898,8 +1904,6 @@ static int fec_enet_mdio_write(struct mii_bus *bus,
> > int mii_id, int regnum,
> > else
> > ret = 0;
> >
> > - reinit_completion(&fep->mdio_done);
> > -
> > if (is_c45) {
> > frame_start = FEC_MMFR_ST_C45;
> >
> > @@ -1911,11 +1915,9 @@ static int fec_enet_mdio_write(struct mii_bus
> > *bus, int mii_id, int regnum,
> > fep->hwp + FEC_MII_DATA);
> >
> > /* wait for end of transfer */
> > - time_left =
> > wait_for_completion_timeout(&fep->mdio_done,
> > - usecs_to_jiffies(FEC_MII_TIMEOUT));
> > - if (time_left == 0) {
> > + ret = fec_enet_mdio_wait(fep);
> > + if (ret) {
> > netdev_err(fep->netdev, "MDIO address write
> > timeout\n");
> > - ret = -ETIMEDOUT;
> > goto out;
> > }
> > } else {
> > @@ -1931,12 +1933,9 @@ static int fec_enet_mdio_write(struct mii_bus
> > *bus, int mii_id, int regnum,
> > fep->hwp + FEC_MII_DATA);
> >
> > /* wait for end of transfer */
> > - time_left = wait_for_completion_timeout(&fep->mdio_done,
> > - usecs_to_jiffies(FEC_MII_TIMEOUT));
> > - if (time_left == 0) {
> > + ret = fec_enet_mdio_wait(fep);
> > + if (ret)
> > netdev_err(fep->netdev, "MDIO write timeout\n");
> > - ret = -ETIMEDOUT;
> > - }
> >
> > out:
> > pm_runtime_mark_last_busy(dev);
> > @@ -2132,6 +2131,9 @@ static int fec_enet_mii_init(struct platform_device
> > *pdev)
> >
> > writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);
> >
> > + /* Clear any pending transaction complete indication */
> > + writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);
> > +
> > fep->mii_bus = mdiobus_alloc();
> > if (fep->mii_bus == NULL) {
> > err = -ENOMEM;
> > @@ -3674,7 +3676,6 @@ fec_probe(struct platform_device *pdev)
> > fep->irq[i] = irq;
> > }
> >
> > - init_completion(&fep->mdio_done);
> > ret = fec_enet_mii_init(pdev);
> > if (ret)
> > goto failed_mii_init;
> > --
> > 2.26.1
>
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