linux-kernel - Re: [PATCH v2 2/7] MIPS: csrc-r4k: Apply verification clocksource flags

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Message-Id: <8d3abbdb-7574-486f-82dd-4213b806a6d8@app.fastmail.com>
Date: Thu, 08 Aug 2024 08:35:35 +0100
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Guenter Roeck" <linux@...ck-us.net>
Cc: "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Serge Semin" <fancer.lancer@...il.com>,
 "Daniel Lezcano" <daniel.lezcano@...aro.org>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "Maciej W. Rozycki" <macro@...am.me.uk>,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
 linux-kernel@...r.kernel.org, regressions@...ts.linux.dev
Subject: Re: [PATCH v2 2/7] MIPS: csrc-r4k: Apply verification clocksource flags

在2024年8月6日八月 下午4:06，Guenter Roeck写道：
> On 8/5/24 22:13, Guenter Roeck wrote:
>> On 8/5/24 22:06, Jiaxun Yang wrote:
>>>
>>>
>>> 在2024年8月6日八月 下午12:09，Guenter Roeck写道：
>>>> Hi,
>>>>
>>>> On Wed, Jun 12, 2024 at 09:54:29AM +0100, Jiaxun Yang wrote:
>>>>> CP0 counter suffers from various problems like SMP sync,
>>>>> behaviour on wait.
>>>>>
>>>>> Set CLOCK_SOURCE_MUST_VERIFY and CLOCK_SOURCE_VERIFY_PERCPU,
>>>>> as what x86 did to TSC, to let kernel test it before use.
>>>>>
>>>>> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>>>
>>> Hi Guenter,
>>>
>>> Thanks for the report, it makes no sense to me though....
>>>
>>> I can't reproduce it with QEMU git master, do you mind specifying your QEMU
>>> version for me? Also is it possible to have a copy of dmesg when failure happens.
>>>
>> 
>> I currently use v9.0.2. I'll try with some other versions tomorrow.
>> A complete log is at
>> https://kerneltests.org/builders/qemu-mips64-master/builds/241/steps/qemubuildcommand/logs/stdio
>> 
>> Are you trying to instantiate an e1000 (or a variant of it) ? So far
>> I have only seen the problem with that controller. There is no specific
>> error message, the network interface just doesn't get an IP address.
>> 
>
> I am able to reproduce the problem with qemu 6.2.0 (Debian build).
> http://server.roeck-us.net/qemu/mips64/ should have everything needed to
> reproduce it. "repeat.sh" repeats the test until it fails.

Thanks for the info, I'm able to reproduce that. It can be reproduced faster
on system with lower CPU performance.

So the actual failure is:

clocksource: timekeeping watchdog on CPU0: Marking clocksource 'MIPS' as unstable because the skew is too large:
clocksource:                       'jiffies' wd_nsec: 500000000 wd_now: ffff8bde wd_last: ffff8bac mask: ffffffff
clocksource:                       'MIPS' cs_nsec: 940634468 cs_now: 310181c4 cs_last: 28090a09 mask: ffffffff
clocksource:                       Clocksource 'MIPS' skewed 440634468 ns (440 ms) over watchdog 'jiffies' interval of 500000000 ns (500 ms)
clocksource:                       'MIPS' is current clocksource.

Jiffies is not an ideal clocksource as watchdog base, really....
I guess clocksource selection process needs to be improved, let me think about it.

>
> Hope this helps,
> Guenter

-- 
- Jiaxun