Date: Thu, 12 Jun 2014 11:57:54 +0800 From: Julian Elischer <julian@freebsd.org> To: "Alexander V. Chernikov" <melifaro@FreeBSD.org>, John Baldwin <jhb@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org, hackers@freebsd.org Subject: Re: Permit init(8) use its own cpuset group. Message-ID: <53992542.3080908@freebsd.org> In-Reply-To: <53988933.5010902@FreeBSD.org> References: <538C8F9A.4020301@FreeBSD.org> <5390DB64.6010704@FreeBSD.org> <53923C09.6020302@FreeBSD.org> <201406091343.39584.jhb@freebsd.org> <53988933.5010902@FreeBSD.org>
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On 6/12/14, 12:52 AM, Alexander V. Chernikov wrote:
> On 09.06.2014 21:43, John Baldwin wrote:
>> On Friday, June 06, 2014 6:09:13 pm Alexander V. Chernikov wrote:
>>> On 06.06.2014 01:04, Alexander V. Chernikov wrote:
>>>> On 05.06.2014 23:59, John Baldwin wrote:
>>>>> On Thursday, June 05, 2014 3:46:15 pm Alexander V. Chernikov wrote:
>>>>>> On 05.06.2014 18:09, John Baldwin wrote:
>>>>>>> On Wednesday, June 04, 2014 3:16:59 pm Alexander V. Chernikov
>>>>>>> wrote:
>>>>>>>> On 04.06.2014 19:06, John Baldwin wrote:
>>>>>>>>> On Monday, June 02, 2014 12:48:50 pm Konstantin Belousov wrote:
>>>>>>>>>> On Mon, Jun 02, 2014 at 06:52:10PM +0400, Alexander V.
>>>>>>>>>> Chernikov wrote:
>>>>>>>>>>> Hello list!
>>>>>>>>>>>
>>>>>>>>>>> Currently init(8) uses group 1 which is root group.
>>>>>>>>>>> Modifications of this group affects both kernel and
>>>>>>>>>>> userland threads.
>>>>>>>>>>> Additionally, such modifications are impossible, for
>>>>>>>>>>> example, in
>>>>>>> presence
>>>>>>>>>>> of multi-queue NIC drivers (like igb or ixgbe) which binds
>>>>>>>>>>> their
>>>>> threads
>>>>>>>>> to
>>>>>>>>>>> particular cpus.
>>>>>>>>>>>
>>>>>>>>>>> Proposed change ("init_cpuset" loader tunable) permits
>>>>>>>>>>> changing cpu
>>>>>>>>>>> masks for
>>>>>>>>>>> userland more easily. Restricting user processes to
>>>>>>>>>>> migrate to/from
>>>>> CPU
>>>>>>>>>>> cores
>>>>>>>>>>> used for network traffic processing is one of the cases.
>>>>>>>>>>>
>>>>>>>>>>> Phabricator: https://phabric.freebsd.org/D141 (the same
>>>>>>>>>>> version
>>>>> attached
>>>>>>>>>>> inline)
>>>>>>>>>>>
>>>>>>>>>>> If there are no objections, I'll commit this next week.
>>>>>>>>>> Why is the tunable needed ?
>>>>>>>>> Because some people already depend on doing 'cpuset -l 0 -s
>>>>>>>>> 1'. It is
>>>>>>> also
>>>>>>>>> documented in our manpages that processes start in cpuset 1
>>>>>>>>> by default
>>>>> so
>>>>>>>>> that you can use 'cpuset -l 0 -s 1' to move all processes, etc.
>>>>>>>>>
>>>>>>>>> For the stated problem (bound ithreads in drivers), I would
>>>>>>>>> actually
>>>>> like
>>>>>>> to
>>>>>>>>> fix ithreads that are bound to a specific CPU to create a
>>>>>>>>> different
>>>>> cpuset
>>>>>>>>> instead so they don't conflict with set 1.
>>>>>>>> Yes, this seem to be much better approach.
>>>>>>>> Please take a look on the new patch (here or in the
>>>>>>>> phabricator).
>>>>>>>> Comments:
>>>>>>>>
>>>>>>>> Use different approach for modifyable root set:
>>>>>>>>
>>>>>>>> * Make sets in 0..15 internal
>>>>>>>> * Define CPUSET_SET1 & CPUSET_ITHREAD in that range
>>>>>>>> * Add cpuset_lookup_builtin() to retrieve such cpu sets by id
>>>>>>>> * Create additional root set for ithreads
>>>>>>>> * Use this set in ithread_create()
>>>>>>>> * Change intr_setaffinity() to use cpuset_iroot (do we
>>>>>>>> really need
>>>>> this)?
>>>>>>>> We can probably do the same for kprocs, but I'm unsure if we
>>>>>>>> really need
>>>>> it.
>>>>>>> I imagined something a bit simpler. Just create a new set in
>>>>> intr_event_bind
>>>>>>> and bind the ithread to the new set. No need to have more
>>>>>>> magic set ids,
>>>>> etc.
>>>>>> Well, we also have userland which can modify given changes via
>>>>>> `cpuset
>>>>>> -x', so we need to be able to add some more logic on set
>>>>>> allocation/keeping. Additionally, we can try to do the same via
>>>>>> `cpuset
>>>>>> -t', so introducing something like cpuset_setIthread() and
>>>>>> hooking into
>>>>>> intr_event_bind() won't probably be enough. At least I can't
>>>>>> think out a
>>>>>> quick and easy way to do this.
>>>>> cpuset -x calls intr_event_bind(). If you just do it there you
>>>>> fix both
>>>>> places.
>>> Yup. I was wrong. This version seems to be simpler while doing the
>>> right
>>> thing.
>> Hmm, I do think this patch is doing the right thing, but I'm
>> worried you
>> might have weird effects, e.g. I worry that because the 'intr' proc
>> is in
>> set 1 still, the thread masks will be (incorrectly) checked when
>> changing
> Well, as far as I understand we don't have any cpu sets bound to
> program ("pid" search returns set of first thread).
> Anyway, each original ithread mask is released via cpuset_rel() so
> I'm a bit unsure about remaining thread masks.
> Playing with cpuset and ixgbe driver, does not reveal given problem:
>
> 12:59 [0] test15# cpuset -g -s 1
> cpuset 1 mask: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
> 16, 17, 18, 19, 20, 21, 22, 23
> 13:00 [0] test15# kldload ixgbe
> 13:00 [0] test15# vmstat -i | grep ix
> irq263: ix0:que 0 116 0
> irq264: ix0:que 1 108 0
> irq265: ix0:que 2 108 0
> irq266: ix0:que 3 108 0
> irq267: ix0:que 4 108 0
> irq268: ix0:que 5 108 0
> irq269: ix0:que 6 108 0
> irq270: ix0:que 7 108 0
> ...
> 13:00 [0] test15# cpuset -g -x 263
> irq 263 mask: 0
> 13:00 [0] test15# cpuset -g -x 264
> irq 264 mask: 1
> 13:00 [0] test15# cpuset -l 21,22,23 -s 1
> 13:01 [0] test15# cpuset -g -s 1
> cpuset 1 mask: 21, 22, 23
> 13:01 [0] test15# cpuset -g -x 263
> irq 263 mask: 0
> 13:01 [0] test15# cpuset -g -x 264
> irq 264 mask: 1
> 13:01 [0] test15# cpuset -l 12 -x 264
> 13:01 [0] test15# cpuset -g -x 264
> irq 264 mask: 12
> 13:01 [0] test15# cpuset -l 22,23 -s 1
> 13:01 [0] test15# echo $?
> 0
> 13:01 [0] test15# cpuset -g -x 264
> irq 264 mask: 12
> 13:01 [0] test15# cpuset -g -s 1
> cpuset 1 mask: 22, 23
>
>
>> set 1 and you still won't be able to 'cpuset -l 0 -s 1'.
>>
>> Also, strictly speaking, it would probably be best to return
>> threads to
>> set 1 when NOCPU is passed to intr_event_bind() to unbind an
>> interrupt.
> Yup.
in a quick look I didn't see anywhere that checked if the old set and
new set are the same set..
>
>
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