svn commit: r277213 - in head: share/man/man9 sys/kern sys/ofed/include/linux sys/sys

[Konstantin Belousov]

On Tue, Jan 20, 2015 at 08:58:34AM +0100, Hans Petter Selasky wrote:
> On 01/20/15 08:51, Konstantin Belousov wrote:
> > On Tue, Jan 20, 2015 at 05:30:25AM +0100, Hans Petter Selasky wrote:
> >> On 01/19/15 22:59, Adrian Chadd wrote:
> >>> Hi,
> >>>
> >>> Would you please check what the results of this are with CPU specific
> >>> callwheels?
> >>>
> >>> I'm doing some 10+ gig traffic testing on -HEAD with RSS enabled (on
> >>> ixgbe) and with this setup, the per-CPU TCP callwheel stuff is
> >>> enabled. But all the callwheels are now back on clock(0) and so is the
> >>> lock contention. :(
> >>>
> >>> Thanks,
> >>>
> >>
> >> Hi,
> >>
> >> Like stated in the manual page, callout_reset_curcpu/on() does not work
> >> with MPSAFE callouts any more!
> > I.e. you 'fixed' some undeterminate bugs in callout migration by not
> > doing migration at all anymore.
> >
> >>
> >> You need to use callout_init_{mtx,rm,rw} and remove the custom locking
> >> inside the callback in the TCP stack to get it working like before!
> >
> > No, you need to do this, if you think that whole callout KPI must be
> > rototiled.  It is up to the person who modifies the KPI, to ensure that
> > existing code is not broken.
> >
> > As I understand, currently we are back to the one-cpu callouts.
> > Do other people consider this situation acceptable ?
> >
> 
> Hi Konstantin,
> 
> Please read the callout 9 manual page first.

Assume I read it.  How this changes any of my points above ?
"""
A change in the CPU selection cannot happen if this function is
re-scheduled inside a callout function. Else the callback function given
by the func argument will be executed on the same CPU like previously
done.
"""
You cannot do this without fixing consumers.