From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Julian Anastasov <ja@ssi.bg>
Cc: Peter Zijlstra <peterz@infradead.org>,
Simon Horman <horms@verge.net.au>,
Eric Dumazet <eric.dumazet@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
lvs-devel@vger.kernel.org, netdev@vger.kernel.org,
netfilter-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
Pablo Neira Ayuso <pablo@netfilter.org>,
Dipankar Sarma <dipankar@in.ibm.com>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper
Date: Thu, 2 May 2013 15:31:07 -0700 [thread overview]
Message-ID: <20130502223107.GB3780@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1305022249010.25417@ja.ssi.bg>
On Thu, May 02, 2013 at 11:19:12PM +0300, Julian Anastasov wrote:
>
> Hello,
>
> On Thu, 2 May 2013, Paul E. McKenney wrote:
>
> > > Only the new cond_resched_rcu() macro provides
> > > PREEMPT_ACTIVE flag to skip the rcu_preempt_sleep_check()
> > > call. The old macros provide locked=0 as you noticed. Does it
> > > answer your question or I'm missing something?
> >
> > PREEMPT_ACTIVE's value is usually 0x10000000. Did it change
> > since 3.9? If not, rcu_sleep_check(preempt_offset & PREEMPT_ACTIVE)
> > is the same as rcu_sleep_check(0).
>
> Yes, the different platforms use different bit,
> that is why I mentioned about my failed attempt at
> changing hardirq.h. PREEMPT_ACTIVE is always != 0.
>
> But I don't understand what do you mean by
> 'preempt_offset & PREEMPT_ACTIVE' being always 0.
> It is always 0 for cond_resched(), cond_resched_lock()
> and cond_resched_softirq(), not for cond_resched_rcu():
>
> (PREEMPT_ACTIVE | PREEMPT_RCU_OFFSET) & PREEMPT_ACTIVE
> should give PREEMPT_ACTIVE, not 0. We have 2 cases in
> rcu_sleep_check() for the if:
>
> 1. !(PREEMPT_ACTIVE) => FALSE for cond_resched_rcu
> 2. !(0) => TRUE for other cond_resched_* macros
>
> On x86 the code is:
>
> __might_sleep:
> pushl %ebp #
> testl $268435456, %ecx #, preempt_offset
> ...
> jne .L240 #,
> // rcu_lock_map checked when PREEMPT_ACTIVE is missing
> .L240:
> // rcu_bh_lock_map checked
OK, apologies -- I was looking at the calls to __might_sleep() in
mainline, and missed the one that you added. Revisiting that, a
question:
> +#ifdef CONFIG_PREEMPT_RCU
> +#define PREEMPT_RCU_OFFSET 1
Does this really want to be "1" instead of PREEMPT_OFFSET?
> +#else
> +#define PREEMPT_RCU_OFFSET PREEMPT_CHECK_OFFSET
> +#endif
> +
> +extern int __cond_resched_rcu(void);
> +
> +#define cond_resched_rcu() ({ \
> + __might_sleep(__FILE__, __LINE__, PREEMPT_ACTIVE | \
> + PREEMPT_RCU_OFFSET); \
> + __cond_resched_rcu(); \
> +})
> +
For the rest, I clearly need to revisit when more alert, because right
now I am not seeing the connection to preemptible RCU's rcu_read_lock()
implementation.
Thanx, Paul
next prev parent reply other threads:[~2013-05-02 22:31 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-30 2:52 [PATCH v2 0/2] sched: Add cond_resched_rcu_lock() helper Simon Horman
2013-04-30 2:52 ` [PATCH v2 1/2] " Simon Horman
2013-04-30 7:12 ` Julian Anastasov
2013-04-30 7:29 ` Simon Horman
2013-04-30 7:52 ` Julian Anastasov
2013-05-01 9:10 ` Peter Zijlstra
2013-05-01 12:46 ` Paul E. McKenney
2013-05-01 14:32 ` Paul E. McKenney
2013-05-02 7:27 ` Peter Zijlstra
2013-05-01 15:17 ` Peter Zijlstra
2013-05-01 15:29 ` Eric Dumazet
2013-05-01 15:59 ` Peter Zijlstra
2013-05-01 16:02 ` Paul E. McKenney
2013-05-01 16:57 ` Peter Zijlstra
2013-05-01 17:30 ` Paul E. McKenney
2013-05-01 14:22 ` Julian Anastasov
2013-05-01 15:55 ` Peter Zijlstra
2013-05-01 18:22 ` Julian Anastasov
2013-05-01 19:04 ` Paul E. McKenney
2013-05-02 7:26 ` Peter Zijlstra
2013-05-02 10:06 ` Julian Anastasov
2013-05-02 15:54 ` Julian Anastasov
2013-05-02 17:32 ` Paul E. McKenney
2013-05-02 18:55 ` Julian Anastasov
2013-05-02 19:24 ` Julian Anastasov
2013-05-02 19:34 ` Paul E. McKenney
2013-05-02 20:19 ` Julian Anastasov
2013-05-02 22:31 ` Paul E. McKenney [this message]
2013-05-03 7:52 ` Julian Anastasov
2013-05-03 16:30 ` Paul E. McKenney
2013-05-03 17:04 ` Peter Zijlstra
2013-05-03 17:34 ` Paul E. McKenney
2013-05-03 18:09 ` Peter Zijlstra
2013-05-03 17:47 ` Julian Anastasov
2013-05-04 7:23 ` Julian Anastasov
2013-05-04 18:03 ` Paul E. McKenney
2013-04-30 2:52 ` [PATCH v2 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping connections Simon Horman
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