From: Alexey Starikovskiy <aystarik@gmail.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: Alexey Starikovskiy <astarikovskiy@suse.de>,
Lin Ming <ming.m.lin@intel.com>, Xiaotian Feng <dfeng@redhat.com>,
"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Len Brown <lenb@kernel.org>,
"Moore, Robert" <robert.moore@intel.com>
Subject: Re: [PATCH -V2] acpi: don't cond_resched if irq is disabled
Date: Fri, 11 Dec 2009 19:25:25 +0300 [thread overview]
Message-ID: <4B227275.5010201@gmail.com> (raw)
In-Reply-To: <20091211161549.GA15760@elf.ucw.cz>
Pavel Machek пишет:
> On Fri 2009-12-11 14:48:21, Alexey Starikovskiy wrote:
>
>> Lin Ming ??????????:
>>
>>> On Thu, 2009-12-10 at 20:21 +0800, Alexey Starikovskiy wrote:
>>>
>>>> Hi Xiaotian,
>>>>
>>>> I think, this is another round of "armor vs. bullet" race... It will hold until
>>>> might_sleep() logic changes again.
>>>>
>>>> Please consider using preemptible() -- IMHO this is the check we should perform
>>>> in our case of voluntary preemption.
>>>>
>>> preemptible() may not work here because it always returns 0 for
>>> non-preemptible kernel.
>>>
>> Right, and it means that this machine does not care about low latency that much.
>> The reason we introduced the preemption point in the first place, was unacceptable latency
>> due to very long AML methods on some machines. We don't need this preemption point for normal
>> operation, this is exactly what voluntary preemption does -- allows those in hurry to pass by.
>> If there are none, fine.
>>
>>> #ifdef CONFIG_PREEMPT
>>> # define preemptible() (preempt_count() == 0 && !irqs_disabled())
>>> # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
>>> #else
>>> # define preemptible() 0
>>> # define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
>>> #endif
>>>
>
> Well, normally we want low latency even for !CONFIG_PREEMPT kernels.
>
> Actually, explicit preemption points are NOPs for CONFIG_PREEMPT
> kernels, right?
> Pavel
>
Right. Do you have code?
Thanks,
Alex.
next prev parent reply other threads:[~2009-12-11 16:25 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-04 4:26 [PATCH] ACPICA: don't cond_resched() when irq_disabled or in_atomic Xiaotian Feng
2009-12-04 5:36 ` Zhang Rui
2009-12-04 5:38 ` Zhang Rui
2009-12-04 6:50 ` Justin Mattock
2009-12-04 7:05 ` Danny Feng
2009-12-04 7:27 ` Justin P. Mattock
2009-12-09 1:54 ` Xiaotian Feng
2009-12-10 10:09 ` Pavel Machek
2009-12-10 11:56 ` [PATCH -V2] acpi: don't cond_resched if irq is disabled Xiaotian Feng
2009-12-10 12:21 ` Alexey Starikovskiy
2009-12-11 5:46 ` Lin Ming
2009-12-11 11:48 ` Alexey Starikovskiy
2009-12-11 16:15 ` Pavel Machek
2009-12-11 16:25 ` Alexey Starikovskiy [this message]
2009-12-11 17:34 ` Pavel Machek
2009-12-28 6:02 ` Xiaotian Feng
2009-12-28 11:12 ` Alexey Starikovskiy
2010-01-16 6:44 ` Len Brown
2009-12-10 17:58 ` [PATCH] ACPICA: don't cond_resched() when irq_disabled or in_atomic Alexey Starikovskiy
2009-12-10 18:18 ` Pavel Machek
2009-12-10 18:37 ` Alexey Starikovskiy
2009-12-10 22:46 ` Justin P. Mattock
2009-12-10 22:54 ` Moore, Robert
2010-01-16 6:46 ` Len Brown
2009-12-11 17:33 ` Pavel Machek
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