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Re: [Xen-devel] [PATCH 2/2] xen: fill topology info for online cpus only


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Thu, 30 Aug 2018 10:46:07 +0200
  • 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: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 30 Aug 2018 08:46:11 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 30/08/18 10:43, Jan Beulich wrote:
>>>> On 30.08.18 at 10:31, <jgross@xxxxxxxx> wrote:
>> On 30/08/18 10:16, Jan Beulich wrote:
>>>>>> On 29.08.18 at 20:23, <jgross@xxxxxxxx> wrote:
>>>> The topology information obtainable via XEN_SYSCTL_cputopoinfo is
>>>> filled rather weird: the size of the array is derived from the highest
>>>> online cpu number, while the data is set to "invalid" for not present
>>>> cpus only.
>>>>
>>>> With smt=0 the information for parked threads is all zero, so it should
>>>> be best to return "invalid" information for offline cpus.
>>>>
>>>> On a dual core system without this patch xl info -n will print:
>>>>
>>>> cpu_topology           :
>>>> cpu:    core    socket     node
>>>>   0:       0        0        0
>>>>   1:       0        0        0
>>>>   2:       1        0        0
>>>
>>> But there's nothing wrong here. The interesting part is what would be
>>> printed for CPU 3 (perhaps on a more than two cores system). After
>>> all topology is valid irrespective of whether a CPU is online - it all
>>> depends on whether the hypervisor still has the information available.
>>> It is for a reason that cpu_smpboot_free() invalidates certain fields
>>> only upon CPU removal:
>>>
>>>     if ( remove )
>>>     {
>>>         c[cpu].phys_proc_id = XEN_INVALID_SOCKET_ID;
>>>         c[cpu].cpu_core_id = XEN_INVALID_CORE_ID;
>>>         c[cpu].compute_unit_id = INVALID_CUID;
>>>
>>> On a 6-core system I see
>>>
>>> cpu:    core    socket     node
>>>   0:       0        0        0
>>>   1:       0        0        0
>>>   2:       1        0        0
>>>   3:       1        0        0
>>>   4:       2        0        0
>>>   5:       2        0        0
>>>   6:       8        0        0
>>>   7:       8        0        0
>>>   8:       9        0        0
>>>   9:       9        0        0
>>>  10:      10        0        0
>>>
>>> which looks fine to me, apart from the missing info on CPU 11.
>>
>> I can change the patch to print the information for the offline cpus
>> (including the now missing ones), too.
>>
>> What is the preferred solution?
> 
> Well, by implication from my earlier reply I think adding the missing
> CPU's info would be better. Let's see what others think.

Okay.

I'll do that and add another patch adding "(offline)" to the output in
case a cpu is offline.


Juergen

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