On Mon, Sep 08, 2014 at 01:20:30PM -0500, Christoph Lameter wrote:
>
> On Thu, 4 Sep 2014, Paul E. McKenney wrote:
>
> > The lglocks use should be of particular interest to you. See above to
> > find the others.
>
> Well the other seem to be in drivers.
OK...
> > Understood, but no hasty chan
On Thu, 4 Sep 2014, Paul E. McKenney wrote:
> The lglocks use should be of particular interest to you. See above to
> find the others.
Well the other seem to be in drivers.
> Understood, but no hasty changes to that part of RCU.
At our age I think we have learned to be very deliberate and slo
On Wed, 3 Sep 2014, Paul E. McKenney wrote:
> As noted earlier, in theory, the atomic operations could be nonatomic,
Well as demonstrated by the patch earlier: The atomic operations are only
used on a the local cpu. There is no synchronization in that sense needed
between processors because ther
On Thu, 4 Sep 2014, Paul E. McKenney wrote:
> So in short, you don't see the potential for this use case actually
> breaking anything, correct?
In general its a performance impact but depending on how this_cpu_ops may
be implemented in a particular platform there may also be correctness
issues si
On Thu, Sep 04, 2014 at 01:19:29PM -0500, Christoph Lameter wrote:
> On Thu, 4 Sep 2014, Paul E. McKenney wrote:
>
> > So in short, you don't see the potential for this use case actually
> > breaking anything, correct?
>
> In general its a performance impact but depending on how this_cpu_ops may
On Thu, Sep 04, 2014 at 10:04:17AM -0500, Christoph Lameter wrote:
>
> On Wed, 3 Sep 2014, Paul E. McKenney wrote:
>
> > As noted earlier, in theory, the atomic operations could be nonatomic,
>
> Well as demonstrated by the patch earlier: The atomic operations are only
> used on a the local cpu.
On Wed, Sep 03, 2014 at 12:43:15PM -0500, Christoph Lameter wrote:
> On Wed, 3 Sep 2014, Paul E. McKenney wrote:
>
> > > Well, a shared data structure would be cleaner in general but there are
> > > certainly other approaches.
> >
> > Per-CPU variables -are- a shared data structure.
>
> No the in
On Wed, 3 Sep 2014, Paul E. McKenney wrote:
> > Well, a shared data structure would be cleaner in general but there are
> > certainly other approaches.
>
> Per-CPU variables -are- a shared data structure.
No the intent is for them to be for the particular cpu and therefore
there is limited suppor
On Wed, Sep 03, 2014 at 10:51:13AM -0500, Christoph Lameter wrote:
> On Wed, 3 Sep 2014, Paul E. McKenney wrote:
>
> > You would prefer that I instead allocated an NR_CPUS-sized array?
>
> Well, a shared data structure would be cleaner in general but there are
> certainly other approaches.
Per-C
On Wed, 3 Sep 2014, Paul E. McKenney wrote:
> You would prefer that I instead allocated an NR_CPUS-sized array?
Well, a shared data structure would be cleaner in general but there are
certainly other approaches.
But lets focus on the dynticks_idle case we are discussing here rather
than tackle t
On Wed, Sep 03, 2014 at 09:10:24AM -0500, Christoph Lameter wrote:
> On Tue, 2 Sep 2014, Paul E. McKenney wrote:
>
> > On Tue, Sep 02, 2014 at 06:22:52PM -0500, Christoph Lameter wrote:
> > > On Tue, 2 Sep 2014, Paul E. McKenney wrote:
> > >
> > > > Yep, these two have been on my "when I am feelin
On Tue, 2 Sep 2014, Paul E. McKenney wrote:
> On Tue, Sep 02, 2014 at 06:22:52PM -0500, Christoph Lameter wrote:
> > On Tue, 2 Sep 2014, Paul E. McKenney wrote:
> >
> > > Yep, these two have been on my "when I am feeling insanely gutsy" list
> > > for quite some time.
> > >
> > > But I have to ask
On Tue, Sep 02, 2014 at 06:22:52PM -0500, Christoph Lameter wrote:
> On Tue, 2 Sep 2014, Paul E. McKenney wrote:
>
> > Yep, these two have been on my "when I am feeling insanely gutsy" list
> > for quite some time.
> >
> > But I have to ask... On x86, is a pair of mfence instructions really
> > c
On Tue, 2 Sep 2014, Paul E. McKenney wrote:
> Yep, these two have been on my "when I am feeling insanely gutsy" list
> for quite some time.
>
> But I have to ask... On x86, is a pair of mfence instructions really
> cheaper than an atomic increment?
Not sure why you would need an mfence instructi
On Tue, Sep 02, 2014 at 03:47:55PM -0500, Christoph Lameter wrote:
> On Tue, 2 Sep 2014, Paul E. McKenney wrote:
>
> > But yes, in theory, something like this can work if appropriate memory
> > barriers are put in place. In practice, this sort of change needs
> > profound testing on multiple arch
On Tue, 2 Sep 2014, Paul E. McKenney wrote:
> But yes, in theory, something like this can work if appropriate memory
> barriers are put in place. In practice, this sort of change needs
> profound testing on multiple architectures.
Ok how can we move forward? I just looked further and it seems a
On Tue, Sep 02, 2014 at 03:14:43PM -0500, Christoph Lameter wrote:
>
> Since dynticks_idle is only ever modified by the local cpu we do
> not need to use an atomic there. The weak "atomicity" of this_cpu
> ops is sufficient since there is no other cpu modifying the variable.
>
> [This is a cautio
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