[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH v3 1/2] xen/link: Introduce .bss.percpu.page_aligned


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 30 Jul 2019 17:36:31 +0100
  • Authentication-results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none; spf=None smtp.pra=andrew.cooper3@xxxxxxxxxx; spf=Pass smtp.mailfrom=Andrew.Cooper3@xxxxxxxxxx; spf=None smtp.helo=postmaster@xxxxxxxxxxxxxxx
  • Autocrypt: addr=andrew.cooper3@xxxxxxxxxx; prefer-encrypt=mutual; keydata= mQINBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABtClBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPokCOgQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86LkCDQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAYkC HwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA==
  • Cc: StefanoStabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Tue, 30 Jul 2019 16:36:42 +0000
  • Ironport-sdr: vdZ2gqpH1L0pMhKx6Q5FtYAzmuMop29skGh6eUOuzcXGX8d4W9pTBU59MQkcPvybbi/J4c1Z46 fPBQwpz0ml8pW2JAq31GSSyqoaU8rQydIGUjYMZ0qG2XFXjudAbrNdiO4z3we2VAbzsnwGLgzs hLn76+0gqZW1I+7qOF7dHvH06QqmylEgVTxr5qKSEc3+nZZmrpC0ERqrI2DaJoz17CcixN9ZcJ hKwJKOt3/AkGbD15ckfBu6GTsftS/O/QZrlv1FB2Hrz3gqsCrgTEbzOg29jSakMrlLhfSwOxjI lnk=
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 30/07/2019 10:49, Jan Beulich wrote:
> On 30.07.2019 11:35, Andrew Cooper wrote:
>> On 30/07/2019 09:42, Jan Beulich wrote:
>>> On 29.07.2019 19:38, Andrew Cooper wrote:
>>>> --- a/xen/arch/x86/xen.lds.S
>>>> +++ b/xen/arch/x86/xen.lds.S
>>>> @@ -293,14 +293,17 @@ SECTIONS
>>>>          __bss_start = .;
>>>>          *(.bss.stack_aligned)
>>>>          *(.bss.page_aligned*)
>>>> -       *(.bss)
>>>> -       . = ALIGN(SMP_CACHE_BYTES);
>>>> +       . = ALIGN(PAGE_SIZE);
>>>>          __per_cpu_start = .;
>>>> +       *(.bss.percpu.page_aligned)
>>>> +       . = ALIGN(PAGE_SIZE);
>>> But this goes too far: What we want is for the TSS to occupy a full
>>> page, not for whatever random other page-aligned object ends up
>>> last here (should any every appear).
>> Come again?  This is ridiculous.
>>
>> Objects in a section following foo.page_aligned should never end up in
>> the tail of the final page of foo.page_aligned, because then they are in
>> the wrong section.
> How do you derive "wrong section"? Sections have an alignment and a
> size. The latter doesn't need to be a multiple of the former. The
> section ends wherever its size says it ends. Using this property is
> actually desirable in other cases, to limit waste of space.

The principle of least surprise, for a section with page_aligned in its
name, is that the section starts and ends on a page boundary.  This is
what people expect when they see a name like that.

It really doesn't matter what is technically possible.  What does matter
is peoples reasonable expectations.

>> A short TSS is a pain to deal with, but even you said you didn't like
>> the xen_tss idea when you suggested it.
>>
>> The name of the section is very deliberately not TSS specific, because
>> there is plenty of other cleanup which will end up with objects in this
>> section.
> Well, if they're all strictly a multiple of PAGE_SIZE, then writing
> down a respective requirement might be acceptable. But even then Inot 
> submitted by me.
> wouldn't be overly happy going that route.

This reply, like most others in this thread, is actively unhelpful, and
I give up.

I can't read your mind.  Neither can anyone else, and noone has the time
to divine what you want.

If you don't come up with something more helpful than "I don't like it
this way", then I'm going to commit this series in its current form, and
you can adjusting it to your own taste, in your own time.

This goes for other series as well, including ones submitted by others. 
It is absolutely critical that review feedback identifies, in a clear
manner, how you expect the issue to be resolved.

For any non-trivial piece of feedback, if it can't be phrased in the
form "I would this patch ok if you alter $X to $Y", then it is probably
wants rethinking.  Whatever the feedback actually is, that gives a
concrete $X which is the perceived problem, and a concrete $Y which is
either a clear discussion point, or a clear direction to work towards.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.