linux-kernel - Re: [PATCH RESEND] Calling check_system_tsc_reliable() before unsynchronized

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Message-ID: <1a53c844-3724-e8e8-2aff-c494a5acb493@oracle.com>
Date:   Fri, 23 Jun 2017 16:30:25 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] Calling check_system_tsc_reliable() before
 unsynchronized_tsc()

在 2017/6/22 21:56, Thomas Gleixner 写道:
> Zhenzhong,
>
> On Wed, 21 Jun 2017, Zhenzhong Duan wrote:
>
> So the patch format is now correct, but the subject line is missing a
> proper subsystem prefix. Please use 'git log 'path/to/patched/file' next
> time to see what the usually used prefix for a file is.
>
> In this case it's:   x86/tsc
>
> Also please do not use [PATCH RESEND] when your patch is different from the
> version you sent before. Please use [PATCH v2] instead.
Got it.
>
>> unsynchronized_tsc() checks value of tsc_clocksource_reliable which is set by
>> check_system_tsc_reliable(). It's better to move check_system_tsc_reliable() at
>> front.
> Please make your statements affirmative. 'It's better' is a weak expression.
>
>> Though X86_FEATURE_CONSTANT_TSC is usually set for TSC reliable system, just in
>> case.
> So what you wanted to say here is:
>
>     tsc_clocksource_reliable is initialized in check_system_tsc_reliable(),
>     but it is checked in unsynchronized_tsc() which is called before the
>     initialization.
>
>     In practice that's not an issue because systems which mark the TSC
>     reliable have X86_FEATURE_CONSTANT_TSC set as well, which is evaluated
>     in unsynchronized_tsc() before tsc_clocksource_reliable.
>
>     Reorder the calls so initialization happens before usage.
Exactly.
>
> All this information is also documented in Documentation/process/.
I'll read them.
>
> No need to resend. I'll fix it up for you this time.
Ok, thanks.

zduan