From: Huang Ying <ying.huang@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, "H.PeterA" <"nvin hpa"@zytor.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andi Kleen <andi@firstfloor.org>
Subject: Re: [RFC][PATCH] irq_work
Date: Fri, 25 Jun 2010 17:17:19 +0800 [thread overview]
Message-ID: <1277457439.3947.184.camel@yhuang-dev.sh.intel.com> (raw)
In-Reply-To: <1277452110.22715.2116.camel@twins>
On Fri, 2010-06-25 at 15:48 +0800, Peter Zijlstra wrote:
> On Fri, 2010-06-25 at 10:12 +0800, Huang Ying wrote:
> >
> > It is better to add "void *data" field in this struct to allow same
> > function can be used for multiple struct irq_work.
>
> No, simply do:
>
> struct my_foo {
> struct irq_work work;
> /* my extra data */
> }
>
> void my_func(struct irq_work *work)
> {
> struct my_foo *foo = container_of(work, struct my_foo, work);
>
> /* tada! */
> }
Yes. This works too. But Adding "void *data" field is helpful if you do
not embed struct irq_work into another struct.
> > And I think IRQ is the implementation detail here, so irq_work is
> > probably not a good name. nmi_return_notifier or nmi_callback is better?
>
> Well, its ran in hard-irq context, so its an irq work. There's nothing
> that says it can only be used from NMI context.
It may be run in other contexts on some system (without APIC). And I
don't think it is useful to others except NMI handler. I think this is a
choice between naming after implementation and purpose.
> > > +void irq_work_run(void)
> > > +{
> > > + struct irq_work *list;
> > > +
> > > + list = xchg(&__get_cpu_var(irq_work_list), CALLBACK_TAIL);
> > > + while (list != CALLBACK_TAIL) {
> > > + struct irq_work *entry = list;
> > > +
> > > + list = list->next;
> > > + entry->func(entry);
> > > +
> > > + entry->next = NULL;
> >
> > entry->next = NULL should be put before entry->func(entry), so that we
> > will not lose a notification from NMI. And maybe check irq_work_list for
> > several times to make sure nothing is lost.
>
> But then _sync() will return before its done executing.
We can use another flag to signify whether it is executing. For example
the bit 0 of entry->next.
> I think clearing after the function is done executing is the only sane
> semantics (and yes, I should fix the current perf code).
>
> You can always miss an NMI since it can always happen before the
> callback gets done, and allowing another enqueue before the callback is
> complete is asking for trouble.
If we move entry->next = NULL before entry->func(entry), we will not
miss the NMI. Can you show how to miss it in this way?
> > > + /*
> > > + * matches the mb in cmpxchg() in irq_work_queue()
> > > + */
> > > + smp_wmb();
> > > + }
> > > +}
> >
> > I don't know why we need smp_wmb() here and smp_rmb() in
> > irq_work_pending(). The smp_<x>mb() in original perf_pending_xxx code is
> > not necessary too. Because smp_<x>mb is invoked in wake_up_process() and
> > __wait_event() already.
>
> The smp_wmb() wants to be before ->next = NULL; so that all writes are
> completed before we release the entry. To that same effect _sync() and
> _queue need the (r)mb.
It is reasonable in this way.
Best Regards,
Huang Ying
next prev parent reply other threads:[~2010-06-25 9:17 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-24 3:04 [RFC 1/5] Make soft_irq NMI safe Huang Ying
2010-06-24 3:04 ` [RFC 2/5] NMI return notifier Huang Ying
2010-06-24 3:04 ` [RFC 3/5] x86, trigger NMI return notifier soft_irq earlier Huang Ying
2010-06-24 6:03 ` Peter Zijlstra
2010-06-24 3:04 ` [RFC 4/5] x86, Use NMI return notifier in MCE Huang Ying
2010-06-24 10:00 ` Andi Kleen
2010-06-24 3:04 ` [RFC 5/5] Use NMI return notifier in perf pending Huang Ying
2010-06-24 6:00 ` Peter Zijlstra
2010-06-24 6:09 ` [RFC 1/5] Make soft_irq NMI safe Peter Zijlstra
2010-06-24 6:45 ` Huang Ying
2010-06-24 6:35 ` [RFC][PATCH] irq_work Peter Zijlstra
2010-06-24 6:43 ` Huang Ying
2010-06-24 6:47 ` Peter Zijlstra
2010-06-24 6:50 ` Huang Ying
2010-06-24 6:58 ` Peter Zijlstra
2010-06-24 7:04 ` Huang Ying
2010-06-24 7:19 ` Peter Zijlstra
2010-06-24 7:27 ` Huang Ying
2010-06-24 7:32 ` Peter Zijlstra
2010-06-24 10:27 ` Andi Kleen
2010-06-24 10:30 ` Peter Zijlstra
2010-06-24 10:52 ` Andi Kleen
2010-06-24 10:58 ` Peter Zijlstra
2010-06-24 11:08 ` Andi Kleen
2010-06-24 11:10 ` Peter Zijlstra
2010-06-24 11:20 ` Andi Kleen
2010-06-24 11:33 ` Peter Zijlstra
2010-06-24 11:55 ` Andi Kleen
2010-06-24 11:57 ` Peter Zijlstra
2010-06-24 12:02 ` Andi Kleen
2010-06-24 12:18 ` Peter Zijlstra
2010-06-24 12:38 ` Andi Kleen
2010-06-25 10:38 ` Peter Zijlstra
2010-06-24 11:42 ` Peter Zijlstra
2010-06-24 11:58 ` Andi Kleen
2010-06-24 12:02 ` Peter Zijlstra
2010-06-24 11:23 ` Ingo Molnar
2010-06-24 11:34 ` Peter Zijlstra
2010-06-24 12:35 ` Ingo Molnar
2010-06-24 13:02 ` Andi Kleen
2010-06-24 13:20 ` Borislav Petkov
2010-06-24 13:33 ` Andi Kleen
2010-06-24 13:42 ` Ingo Molnar
2010-06-24 13:46 ` Ingo Molnar
2010-06-24 14:01 ` Andi Kleen
2010-06-24 15:41 ` Borislav Petkov
2010-06-24 16:09 ` Andi Kleen
2010-06-25 2:12 ` Huang Ying
2010-06-25 7:48 ` Peter Zijlstra
2010-06-25 9:17 ` Huang Ying [this message]
2010-06-25 9:23 ` Frederic Weisbecker
2010-06-25 9:30 ` Huang Ying
2010-06-25 9:44 ` Frederic Weisbecker
2010-06-25 9:30 ` Peter Zijlstra
2010-06-25 11:58 ` huang ying
2010-06-25 9:08 ` Andi Kleen
2010-06-25 18:30 ` [RFC][PATCH] irq_work -v2 Peter Zijlstra
2010-06-25 19:30 ` Andi Kleen
2010-06-25 19:39 ` Peter Zijlstra
2010-06-25 19:49 ` Peter Zijlstra
2010-06-25 22:29 ` Andi Kleen
2010-06-26 8:36 ` Peter Zijlstra
2010-06-26 10:08 ` Andi Kleen
2010-06-26 10:32 ` Peter Zijlstra
2010-06-25 19:47 ` Peter Zijlstra
2010-06-26 1:26 ` huang ying
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