Thanks Jacob, and Richard for your comments.
I've replied re: details of the patch on the Wired LAN. Thanks for
generating + submitting the patch across the related drivers too!
I agree on bumping the counter when we can't grab the lock, more comments
over on the Intel list.
Cheers,
- DavidM
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On 28 April 2017 at 09:58, Keller, Jacob E <[email protected]> wrote:
>
>
> > -----Original Message-----
> > From: Keller, Jacob E [mailto:[email protected]]
> > Sent: Thursday, April 27, 2017 3:58 PM
> > To: Richard Cochran <[email protected]>; David Mirabito
> > <[email protected]>
> > Cc: [email protected]
> > Subject: Re: [Linuxptp-devel] Workaround for 'timed out while polling
> for tx
> > timestamp' on IGB
> >
> > > -----Original Message-----
> > > From: Richard Cochran [mailto:[email protected]]
> > > Sent: Thursday, April 27, 2017 11:25 AM
> > > To: David Mirabito <[email protected]>
> > > Cc: [email protected]
> > > Subject: Re: [Linuxptp-devel] Workaround for 'timed out while polling
> for tx
> > > timestamp' on IGB
> > >
> > > On Thu, Apr 27, 2017 at 03:41:03PM +1000, David Mirabito wrote:
> > > > * "Fixing" (if this is indeed a bug) was reasonably straight forward
> - more
> > > > or less reordering steps 4,5,6 so that we wake the app only *after*
> we've
> > > > unlocked the bit.
> > >
> > > If your analysis was correct, then yes, indeed this is a driver bug.
> > > Please submit a patch on netdev.
> > >
> >
> > Can I clarify here, David, you're suggesting that you instead clear the
> bitlock
> > earlier before you call the timestamp function? I think that's probably
> a good
> > thing and minimizing the time that we hold a lock is good. I suspect
> that most of
> > the Intel drivers are at fault here and can make some patches for them.
> Or you
> > can if you wish.
> >
> > There *is* a fundamental limit that the hardware assumes that only one
> transmit
> > timestamp request at a time, so we can't actually do any better. But we
> can
> > unlock as soon as we read the timestamp registers, which should help
> this race.
> >
> > Thanks,
> > Jake
>
> I sent a patch to Intel Wired LAN, and I Cc'd both of you on it. Feel free
> to comment. I fixed up e1000e, igb, ixgbe, and i40e. Please comment
> indicating if you think this fix is correct. I believe it is correct from
> your original comment.
>
> One change we could make as well, is to increment the timestamp dropped
> counter for Tx whenever we get a request that we can't fulfill, but I
> didn't change that in my current patch.
>
> Thanks,
> Jake
>
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