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SubjectRe: are ioctl calls supposed to take this long?
On Fri, 6 Jul 2001, Chris Friesen wrote:

> "Richard B. Johnson" wrote:
> >
> > On Fri, 6 Jul 2001, Chris Friesen wrote:
> >
> > > I am using the following snippet of code to find out some information about the
> > > MII PHY interface of my ethernet device (which uses the tulip driver). When I
> > > did some timing measurements with gettimeofday() I found that the ioctl call
> > > takes a bit over a millisecond to complete. This seems to me to be an awfully
> > > long time for what should be (as far as I can see) a very simple operation.
>
> > It's not ioctl() overhead, it's what has to be done in the driver to
> > get the information you request.
> >
> > (1) Stop the chip
> > (2) Read the media interface using an awful SERIAL protocol in which
> > you manipulate 3 bits using multiple instructions, to send
> > or receive a single BIT (not BYTE) of data. You do the 8 times
> > per byte.
> > (3) Restart the chip.
>
> Are you sure about this? In the tulip.c driver the following appears to be the
> salient code:
>
> static int private_ioctl(struct device *dev, struct ifreq *rq, int cmd)
> {
> struct tulip_private *tp = (struct tulip_private *)dev->priv;
> long ioaddr = dev->base_addr;
> u16 *data = (u16 *)&rq->ifr_data;
> int phy = tp->phys[0] & 0x1f;
> long flags;
>
> switch(cmd) {
> case SIOCDEVPRIVATE: /* Get the address of the PHY in use. */
> if (tp->mii_cnt)
> data[0] = phy;
> else if (tp->flags & HAS_NWAY143)
> data[0] = 32;
> else if (tp->chip_id == COMET)
> data[0] = 1;
> else
> return -ENODEV;
>
..... This falls through to
SIOCDEVPRIVATE+1

>
> I don't see any device stopping or reading of the media interface here. Now
> there may be something very subtle hidden somewhere that I'm not seeing, but
> this looks like some relatively straightforward comparisons.

Look at tulip_mdio_read() and the zillions of times it's called.
It's called in SIOCDEVPRIVATE+1 when SIOCDEVPRIVATE falls through.
It falls through always, unless there is the -ENODEV error.
tulip_mdio_read() does the bit-banging junk.



Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).

I was going to compile a list of innovations that could be
attributed to Microsoft. Once I realized that Ctrl-Alt-Del
was handled in the BIOS, I found that there aren't any.


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