Re: [PATCHv2] lib/ratelimit: Lockless ratelimiting

From: Dmitry Safonov <dima@arista.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>, Arnd Bergmann <arnd@arndb.de>,
	David Airlie <airlied@linux.ie>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	intel-gfx@lists.freedesktop.org,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	dri-devel@lists.freedesktop.org,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCHv2] lib/ratelimit: Lockless ratelimiting
Date: Tue, 03 Jul 2018 21:59:14 +0100	[thread overview]
Message-ID: <1530651554.3205.37.camel@arista.com> (raw)
In-Reply-To: <CAHp75VfxajbTK3azfRWVBY6+f91JjGZwzHKrhQcHXDw9xeO_HA@mail.gmail.com>

On Tue, 2018-06-26 at 21:41 +0300, Andy Shevchenko wrote:
> > > > @@ -42,9 +41,10 @@ static inline void
> > > > ratelimit_state_init(struct
> > > > ratelimit_state *rs,
> > > >  {
> > > >         memset(rs, 0, sizeof(*rs));
> > > > 
> > > > -       raw_spin_lock_init(&rs->lock);
> > > >         rs->interval    = interval;
> > > >         rs->burst       = burst;
> > > > +       atomic_set(&rs->printed, 0);
> > > > +       atomic_set(&rs->missed, 0);
> > > 
> > > Can it be
> > > 
> > > *rs = RATELIMIT_STATE_INIT(interval, burst);
> > > 
> > > ?
> > > 
> > > (Yes, the '(struct ratelimit_state)' has to be added to macro to
> > > allow this)
> > 
> > Sure.
> 
> This part, by the way, potentially can be split into preparatory
> patch. Please, double check if it possible to do this way.

Hmm, I tried this way:
:#define RATELIMIT_STATE_INIT(name, interval_init, burst_init) ({ \
:               struct ratelimit_state name = {                   \
:                       .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \
:                       .interval       = interval_init,          \
:                       .burst          = burst_init,             \
:               };                                                \
:               name;                                             \
:       })

but the expression becomes non-constant, so it fails to compile in
definitions of globals.

I think I'll change it to
struct ratelimit_state tmp = RATELIMIT_STATE_INIT(...);
*rs = tmp;

Not perfect, but we did memset() and set elements after, so it's kinda
the same.

-- 
Thanks,
             Dmitry
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