Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature

From	Byungchul Park <byungchul.park@lge.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature
Date	2017-03-01 06:30 +0100
Message-ID	<tg4ZQ-6FG-1@gated-at.bofh.it> (permalink)
References	<t0YjD-4z4-5@gated-at.bofh.it> <t0Ytl-4D1-41@gated-at.bofh.it> <tfPR9-4Up-35@gated-at.bofh.it> <tfQNc-5z5-7@gated-at.bofh.it> <tfUQO-8fZ-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Tue, Feb 28, 2017 at 07:29:02PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 28, 2017 at 10:24:44PM +0900, Byungchul Park wrote:
> > On Tue, Feb 28, 2017 at 02:10:12PM +0100, Peter Zijlstra wrote:
> 
> > > > +/* For easy access to xhlock */
> > > > +#define xhlock(t, i)		((t)->xhlocks + (i))
> > > > +#define xhlock_prev(t, l)	xhlock(t, idx_prev((l) - (t)->xhlocks))
> > > > +#define xhlock_curr(t)		xhlock(t, idx(t))
> > > 
> > > So these result in an xhlock pointer
> > > 
> > > > +#define xhlock_incr(t)		({idx(t) = idx_next(idx(t));})
> > > 
> > > This does not; which is confusing seeing how they share the same
> > > namespace; also incr is weird.
> > 
> > OK.. Could you suggest a better name? xhlock_adv()? advance_xhlock()?
> > And.. replace it with a function?
> 
> How about doing: xhlocks_idx++ ? That is, keep all the indexes as
> regular u32 and only reduce the space when using them as index.

OK.

> 
> Also, I would write the loop:
> 
> > +static int commit_xhlocks(struct cross_lock *xlock)
> > +{
> > +     struct task_struct *curr = current;
> > +     struct hist_lock *xhlock_c = xhlock_curr(curr);
> > +     struct hist_lock *xhlock = xhlock_c;
> > +
> > +     do {
> > +             xhlock = xhlock_prev(curr, xhlock);
> > +
> > +             if (!xhlock_used(xhlock))
> > +                     break;
> > +
> > +             if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
> > +                     break;
> > +
> > +             if (same_context_xhlock(xhlock) &&
> > +                 before(xhlock->prev_gen_id, xlock->hlock.gen_id) &&
> > +                 !commit_xhlock(xlock, xhlock))
> > +                     return 0;
> > +     } while (xhlock_c != xhlock);
> > +
> > +     return 1;
> > +}
> 
> like:
> 
> #define xhlock(i)	current->xhlocks[i % MAX_XHLOCKS_NR]
> 
> 	for (i = 0; i < MAX_XHLOCKS_NR; i++) {
> 		xhlock = xhlock(curr->xhlock_idx - i);
> 
> 		/* ... */
> 	}
> 
> That avoids that horrible xhlock_prev() thing.

Right. I decided to force MAX_XHLOCKS_NR to be power of 2 and everything
became easy. Thank you very much.

Thread

Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-02-28 14:20 +0100
  Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-02-28 15:20 +0100
    Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-02-28 19:40 +0100
      Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-03-01 06:30 +0100
        Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-03-01 12:20 +0100
          Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-03-01 14:00 +0100

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