From: "Richard B. Johnson" <root@chaos.analogic.com>
To: Chris Friesen <cfriesen@nortelnetworks.com>
Cc: "Friesen,
Christopher [CAR:VS16:EXCH]" <cfriesen@americasm01.nt.com>,
linux-kernel@vger.kernel.org
Subject: Re: are ioctl calls supposed to take this long?
Date: Fri, 6 Jul 2001 11:32:58 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.3.95.1010706112457.1472A-100000@chaos.analogic.com> (raw)
In-Reply-To: <3B45D5DF.17D2B3F8@nortelnetworks.com>
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.
next prev parent reply other threads:[~2001-07-06 15:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-06 13:34 are ioctl calls supposed to take this long? Chris Friesen
2001-07-06 14:41 ` Richard B. Johnson
2001-07-06 15:14 ` Chris Friesen
2001-07-06 15:32 ` Richard B. Johnson [this message]
2001-07-06 15:40 ` Chris Friesen
2001-07-06 18:26 ` why this 1ms delay in mdio_read? (cont'd from "are ioctl calls supposed to take this long?") Chris Friesen
2001-07-06 18:48 ` Richard B. Johnson
2001-07-06 19:35 ` Chris Friesen
2001-07-06 21:41 ` Donald Becker
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