Re: [PATCH 1/3] pci: VPD access timeout increase

From: Stephen Hemminger
Date: Thu Sep 04 2008 - 12:32:53 EST


On Thu, 4 Sep 2008 15:19:46 +0100
Ben Hutchings <bhutchings@xxxxxxxxxxxxxx> wrote:

> Matthew Wilcox wrote:
> > On Wed, Sep 03, 2008 at 03:57:13PM -0700, Stephen Hemminger wrote:
> > > Accessing the VPD area can take a long time. There are comments in the
> > > SysKonnect vendor driver that it can take up to 25ms. The existing vpd
> > > access code fails consistently on my hardware.

It's bad but not that bad more details are:

MIN MAX
-------------------------------------------------------------------
write 1.8 ms 3.6 ms
internal write cyles 0.7 ms 7.0 ms
-------------------------------------------------------------------
over all program time 2.5 ms 10.6 ms
read 1.3 ms 2.6 ms
-------------------------------------------------------------------
over all 3.8 ms 13.2 ms


Usable VPD is limited to 2K so worst case read is 27 seconds.
Note: there doesn't appear to be an standard for VPD size register in
PCI spec, but there is a device specific register.

> > Wow, that's slow. If you were to try to read all 32k, it'd take more
> > than three minutes! (I presume it doesn't actually have as much as 32k).
> >
> > > Change the access routines to:
> > > * use a mutex rather than spinning with IRQ's disabled and lock held
> > > * have a longer timeout
> > > * call schedule while spinning to provide some responsivness
> >
> > I agree with your approach, but have one minor comment:
> >
> > > - spin_lock_irq(&vpd->lock);
> > > + mutex_lock(&vpd->lock);
> >
> > This should be:
> >
> > + if (mutex_lock_interruptible(&vpd->lock))
> > + return -EINTR;
> [...]
>
> This is fine for the sysfs case, but not if this is called during device
> probe - we don't want signals to modprobe to break device initialisation,
> do we?

Why not, it makes sense to allow killing a stuck modprobe.
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