Re: [PATCH] perf_events: fix event scheduling issues introduced by transactional API (take 2)

[Lin Ming <ming.m.lin@intel.com>]

On Tue, 2010-05-25 at 23:32 +0800, Peter Zijlstra wrote:
> On Tue, 2010-05-25 at 17:02 +0200, Stephane Eranian wrote:
> > Ok, the patch look good expect it needs:
> > 
> > static int x86_pmu_commit_txn(const struct pmu *pmu)
> > {
> >         ......
> >         /*
> >          * copy new assignment, now we know it is possible
> >          * will be used by hw_perf_enable()
> >          */
> >         memcpy(cpuc->assign, assign, n*sizeof(int));
> > 
> >         cpuc->n_txn = 0;
> > 
> >         return 0;
> > }
> > 
> > Because you always call cancel_txn() even when commit()
> > succeeds. I don't really understand why. I think it could be
> > avoided by clearing the group_flag in commit_txn() if it
> > succeeds. It would also make the logical flow more natural. Why
> > cancel something that has succeeded. You cancel when you fail/abort.
> 
> Gah, I forgot about that. I think I suggested to Lin to do that and then
> promptly forgot.

cancel_txn() clears the transaction flag, so it is needed after both
success and fail transaction, although the function name is a bit
misleading.

Peter's patch adds the clear of transaction flag into each
implementation of ->commit_txn.

So cancel_txn() is only called after fail transaction now.

Thanks,
Lin Ming

> 
> Let me add that and at least push this patch fwd, we can try and clean
> up that detail later on.