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Re: [Xen-devel] [PATCH] xen: Fix x86 sched_clock() interface for xen


  • To: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, x86@xxxxxxxxxx
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Fri, 11 Jan 2019 08:31:03 +0100
  • Autocrypt: addr=jgross@xxxxxxxx; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb
  • Cc: sstabellini@xxxxxxxxxx, stable@xxxxxxxxxxxxxxx, hans@xxxxxxxxxxx, mingo@xxxxxxxxxx, bp@xxxxxxxxx, hpa@xxxxxxxxx, tglx@xxxxxxxxxxxxx
  • Delivery-date: Fri, 11 Jan 2019 07:31:24 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 11/01/2019 08:15, Juergen Gross wrote:
> On 11/01/2019 00:10, Boris Ostrovsky wrote:
>> On 1/10/19 12:17 PM, Boris Ostrovsky wrote:
>>> On 1/10/19 11:14 AM, Juergen Gross wrote:
>>>> On 10/01/2019 16:34, Boris Ostrovsky wrote:
>>>>> On 1/10/19 5:07 AM, Juergen Gross wrote:
>>>>>>  
>>>>>> +void xen_clocksource_suspend(void)
>>>>>> +{
>>>>>> +        xen_clock_value_saved = xen_clocksource_read() - 
>>>>>> xen_sched_clock_offset;
>>>>> xen_clock_value_saved = xen_sched_clock() maybe? 
>>>> I wanted xen_clocksource_suspend() and xen_clocksource_resume() to
>>>> be symmetrical to each other.
>>> OK.
>>>
>>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>>>
>>>> In case you are feeling strong about that, I'm not. :-) So in case
>>>> you insist on it I can change it. Or you can do so while committing.
>>
>>
>> I did some basic testing and noticed this (at loglevel=8):
>>
>> [   64.336488] Freezing user space processes ... (elapsed 0.001 seconds)
>> done.
>> [   64.337805] OOM killer disabled.
>> [   64.337814] Freezing remaining freezable tasks ... (elapsed 0.000
>> seconds) done.
>> [   64.339066] suspending xenstore...
>> [   85.888340] xen:grant_table: Grant tables using version 1 layout
>> [   64.359729] OOM killer enabled.
>> [   64.359736] Restarting tasks ... done.
>>
>>
>> Which made me think that perhaps we should do suspend/restore of the
>> clocksource as close as possible to HYPERVISOR_suspend() call, e.g. in
>> xen_arch_pre_suspend()/xen_arch_post_suspend():
>>
>> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
>> index 45fc9caf3880..80ecba3fcc8c 100644
>> --- a/arch/x86/xen/suspend.c
>> +++ b/arch/x86/xen/suspend.c
>> @@ -22,6 +22,7 @@ static DEFINE_PER_CPU(u64, spec_ctrl);
>>  
>>  void xen_arch_pre_suspend(void)
>>  {
>> +       xen_clocksource_suspend();
>>         xen_save_time_memory_area();
>>  
>>         if (xen_pv_domain())
>> @@ -36,6 +37,7 @@ void xen_arch_post_suspend(int cancelled)
>>                 xen_hvm_post_suspend(cancelled);
>>  
>>         xen_restore_time_memory_area();
>> +       xen_clocksource_resume();
>>  }
>>  
>>  static void xen_vcpu_notify_restore(void *data)
>>
>>
>> This still has a window of incorrect clock value (you can see it, for
>> example, when xen_hvm_post_suspend() does pr_info("Xen HVM callback
>> vector for event delivery is enabled\n")), but it's smaller than before.
>> In particular, we will make time right before dpm_resume_start() call.
> 
> You are right, this is better.

In fact, I can just handle this entirely inside arch/x86/xen/time.c by
moving the required statements into xen_save_time_memory_area() and
xen_restore_time_memory_area().


Juergen

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