From: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
To: Marc Zyngier <marc.zyngier@arm.com>,
Florian Fainelli <f.fainelli@gmail.com>,
Doug Berger <opendmb@gmail.com>
Cc: Mans Rullgard <mans@mansr.com>, Mason <slash.tmp@free.fr>,
Thomas Gleixner <tglx@linutronix.de>,
Jason Cooper <jason@lakedaemon.net>,
LKML <linux-kernel@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback
Date: Mon, 21 Aug 2017 15:25:20 +0200 [thread overview]
Message-ID: <a0dc9054-9c37-cc3b-eca5-f68080d5731c@sigmadesigns.com> (raw)
In-Reply-To: <ee3119ec-75e9-376d-f1f1-630a9a17c660@arm.com>
On 07/08/2017 14:56, Marc Zyngier wrote:
> On 28/07/17 15:06, Marc Gonzalez wrote:
>
>> On 27/07/2017 20:17, Florian Fainelli wrote:
>>
>>> On 07/26/2017 12:13 PM, Måns Rullgård wrote:
>>>
>>>> Florian Fainelli writes:
>>>>
>>>>> On 07/25/2017 06:29 AM, Måns Rullgård wrote:
>>>>>
>>>>>> Marc Gonzalez writes:
>>>>>>
>>>>>>> On 25/07/2017 15:16, Måns Rullgård wrote:
>>>>>>>
>>>>>>>> What happened to the patch adding the proper combined function?
>>>>>>>
>>>>>>> It appears you're not CCed on v2.
>>>>>>>
>>>>>>> https://patchwork.kernel.org/patch/9859799/
>>>>>>>
>>>>>>> Doug wrote:
>>>>>>>> Yes, you understand correctly. The irq_mask_ack method is entirely
>>>>>>>> optional and I assume that is why this issue went undetected for so
>>>>>>>> long; however, it is slightly more efficient to combine the functions
>>>>>>>> (even if the ack is unnecessary) which is why I chose to do so for my
>>>>>>>> changes to the irqchip-brcmstb-l2 driver where I first discovered this
>>>>>>>> issue. How much value the improved efficiency has is certainly
>>>>>>>> debatable, but interrupt handling is one area where people might care
>>>>>>>> about such a small difference. As the irqchip-tango driver maintainer
>>>>>>>> you are welcome to decide whether or not the irq_mask_ack method makes
>>>>>>>> sense to you.
>>>>>>>
>>>>>>> My preference goes to leaving the irq_mask_ack callback undefined,
>>>>>>> and let the irqchip framework use irq_mask and irq_ack instead.
>>>>>>
>>>>>> Why would you prefer the less efficient way?
>>>>>
>>>>> Same question here, that does not really make sense to me.
>>>>>
>>>>> The whole point of this patch series is to have a set of efficient and
>>>>> bugfree (or nearly) helper functions that drivers can rely on, are you
>>>>> saying that somehow using irq_mask_and_ack is exposing a bug in the
>>>>> tango irqchip driver and using the separate functions does not expose
>>>>> this bug?
>>>>
>>>> There is currently a bug in that the function used doesn't do what its
>>>> name implies which can't be good. Using the separate mask and ack
>>>> functions obviously works, but combining them saves a lock/unlock
>>>> sequence. The correct combined function has already been written, so I
>>>> see no reason not to use it.
>>>
>>> Marc/Mason, are you intending to get this patch accepted in order to
>>> provide a quick bugfix targeting earlier kernels with the tango irqchip
>>> driver or is this how you think the correct fix for the tango irqchip
>>> driver is as opposed to using Doug's fix?
>>
>> Hello Florian,
>>
>> I am extremely grateful for you and Doug bringing the defect to
>> my attention, as it was indeed causing an issue which I had not
>> found the time to investigate.
>>
>> The reason I proposed an alternate patch is that
>> 1) Doug didn't seem to mind, 2) simpler code leads to fewer bugs
>> and less maintenance IME, and 3) I didn't see many drivers using
>> the irq_mask_ack() callback (9 out of 86) with a few misusing it,
>> by defining irq_mask = irq_mask_ack.
>>
>> As you point out, my patch might be slightly easier to backport
>> than Doug's (TBH, I hadn't considered that aspect until you
>> mentioned it).
>>
>> Has anyone ever quantified the performance improvement of
>> mask_ack over mask + ack?
>
> Aren't you the one who is in position of measuring this effect on the
> actual HW that uses this?
Using separate mask and ack functions (i.e. my patch)
# iperf3 -c 172.27.64.110 -t 20
Connecting to host 172.27.64.110, port 5201
[ 4] local 172.27.64.1 port 40868 connected to 172.27.64.110 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 106 MBytes 888 Mbits/sec 18 324 KBytes
[ 4] 1.00-2.00 sec 106 MBytes 885 Mbits/sec 0 361 KBytes
[ 4] 2.00-3.00 sec 105 MBytes 883 Mbits/sec 4 279 KBytes
[ 4] 3.00-4.00 sec 106 MBytes 890 Mbits/sec 0 300 KBytes
[ 4] 4.00-5.00 sec 106 MBytes 887 Mbits/sec 0 310 KBytes
[ 4] 5.00-6.00 sec 105 MBytes 883 Mbits/sec 0 315 KBytes
[ 4] 6.00-7.00 sec 105 MBytes 885 Mbits/sec 0 321 KBytes
[ 4] 7.00-8.00 sec 105 MBytes 880 Mbits/sec 0 325 KBytes
[ 4] 8.00-9.00 sec 106 MBytes 888 Mbits/sec 0 329 KBytes
[ 4] 9.00-10.00 sec 106 MBytes 886 Mbits/sec 0 335 KBytes
[ 4] 10.00-11.00 sec 105 MBytes 885 Mbits/sec 0 351 KBytes
[ 4] 11.00-12.00 sec 106 MBytes 887 Mbits/sec 1 276 KBytes
[ 4] 12.00-13.00 sec 106 MBytes 885 Mbits/sec 0 321 KBytes
[ 4] 13.00-14.00 sec 105 MBytes 883 Mbits/sec 0 349 KBytes
[ 4] 14.00-15.00 sec 106 MBytes 890 Mbits/sec 0 366 KBytes
[ 4] 15.00-16.00 sec 106 MBytes 888 Mbits/sec 2 286 KBytes
[ 4] 16.00-17.00 sec 105 MBytes 884 Mbits/sec 0 303 KBytes
[ 4] 17.00-18.00 sec 105 MBytes 883 Mbits/sec 0 311 KBytes
[ 4] 18.00-19.00 sec 105 MBytes 880 Mbits/sec 0 315 KBytes
[ 4] 19.00-20.00 sec 106 MBytes 890 Mbits/sec 0 321 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-20.00 sec 2.06 GBytes 885 Mbits/sec 25 sender
Using combined mask and ack functions (i.e. Doug's patch)
# iperf3 -c 172.27.64.110 -t 20
Connecting to host 172.27.64.110, port 5201
[ 4] local 172.27.64.1 port 41235 connected to 172.27.64.110 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 107 MBytes 897 Mbits/sec 60 324 KBytes
[ 4] 1.00-2.00 sec 107 MBytes 898 Mbits/sec 0 361 KBytes
[ 4] 2.00-3.00 sec 107 MBytes 898 Mbits/sec 39 194 KBytes
[ 4] 3.00-4.00 sec 107 MBytes 895 Mbits/sec 0 214 KBytes
[ 4] 4.00-5.00 sec 107 MBytes 901 Mbits/sec 0 223 KBytes
[ 4] 5.00-6.00 sec 108 MBytes 902 Mbits/sec 0 230 KBytes
[ 4] 6.00-7.00 sec 107 MBytes 895 Mbits/sec 0 242 KBytes
[ 4] 7.00-8.00 sec 107 MBytes 901 Mbits/sec 0 253 KBytes
[ 4] 8.00-9.00 sec 107 MBytes 899 Mbits/sec 0 264 KBytes
[ 4] 9.00-10.00 sec 108 MBytes 903 Mbits/sec 0 276 KBytes
[ 4] 10.00-11.00 sec 108 MBytes 902 Mbits/sec 0 286 KBytes
[ 4] 11.00-12.00 sec 107 MBytes 899 Mbits/sec 0 300 KBytes
[ 4] 12.00-13.00 sec 107 MBytes 898 Mbits/sec 33 247 KBytes
[ 4] 13.00-14.00 sec 107 MBytes 900 Mbits/sec 0 294 KBytes
[ 4] 14.00-15.00 sec 107 MBytes 900 Mbits/sec 0 325 KBytes
[ 4] 15.00-16.00 sec 107 MBytes 899 Mbits/sec 0 342 KBytes
[ 4] 16.00-17.00 sec 107 MBytes 898 Mbits/sec 0 351 KBytes
[ 4] 17.00-18.00 sec 108 MBytes 902 Mbits/sec 0 355 KBytes
[ 4] 18.00-19.00 sec 107 MBytes 901 Mbits/sec 0 359 KBytes
[ 4] 19.00-20.00 sec 108 MBytes 903 Mbits/sec 32 255 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-20.00 sec 2.09 GBytes 900 Mbits/sec 164 sender
Ergo, it seems that the performance improvement of the combined
implementation is approximately 1.5% for a load generating ~80k
interrupts per second.
I suppose a 1.5% improvement for free should not be ignored.
Therefore, I rescind my v3 patch.
Doug/Florian, thanks again for fixing the tango driver.
Regards.
next prev parent reply other threads:[~2017-08-21 13:25 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-19 19:07 [PATCH v2 0/6] Add support for BCM7271 style interrupt controller Doug Berger
2017-07-19 19:07 ` [PATCH v2 1/6] genirq: generic chip: add irq_gc_mask_disable_and_ack_set() Doug Berger
2017-07-19 19:07 ` [PATCH v2 2/6] irqchip/tango: Use irq_gc_mask_disable_and_ack_set Doug Berger
2017-07-24 16:40 ` Marc Gonzalez
2017-07-24 17:54 ` Doug Berger
2017-07-25 13:08 ` [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback Marc Gonzalez
2017-07-25 13:16 ` Måns Rullgård
2017-07-25 13:26 ` Marc Gonzalez
2017-07-25 13:29 ` Måns Rullgård
2017-07-26 18:20 ` Florian Fainelli
2017-07-26 19:13 ` Måns Rullgård
2017-07-27 18:17 ` Florian Fainelli
2017-07-28 14:06 ` Marc Gonzalez
2017-08-07 12:56 ` Marc Zyngier
2017-08-18 18:24 ` Florian Fainelli
2017-08-19 16:05 ` Måns Rullgård
2017-08-21 13:25 ` Marc Gonzalez [this message]
2017-09-18 8:49 ` Marc Gonzalez
2017-07-25 14:15 ` Marc Gonzalez
2017-07-19 19:07 ` [PATCH v2 3/6] genirq: generic chip: remove irq_gc_mask_disable_reg_and_ack() Doug Berger
2017-07-19 19:07 ` [PATCH v2 4/6] irqchip: brcmstb-l2: Remove some processing from the handler Doug Berger
2017-07-19 19:07 ` [PATCH v2 5/6] irqchip: brcmstb-l2: Abstract register accesses Doug Berger
2017-07-19 19:07 ` [PATCH v2 6/6] irqchip: brcmstb-l2: Add support for the BCM7271 L2 controller Doug Berger
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