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Re: [Xen-devel] [PATCH RFC 08/49] xen/sched: use new sched_item instead of vcpu in scheduler interfaces


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Mon, 1 Apr 2019 08:06:48 +0200
  • Autocrypt: addr=jgross@xxxxxxxx; prefer-encrypt=mutual; keydata= mQENBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAG0H0p1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmNvbT6JATkEEwECACMFAlOMcK8CGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRCw3p3WKL8TL8eZB/9G0juS/kDY9LhEXseh mE9U+iA1VsLhgDqVbsOtZ/S14LRFHczNd/Lqkn7souCSoyWsBs3/wO+OjPvxf7m+Ef+sMtr0 G5lCWEWa9wa0IXx5HRPW/ScL+e4AVUbL7rurYMfwCzco+7TfjhMEOkC+va5gzi1KrErgNRHH kg3PhlnRY0Udyqx++UYkAsN4TQuEhNN32MvN0Np3WlBJOgKcuXpIElmMM5f1BBzJSKBkW0Jc Wy3h2Wy912vHKpPV/Xv7ZwVJ27v7KcuZcErtptDevAljxJtE7aJG6WiBzm+v9EswyWxwMCIO RoVBYuiocc51872tRGywc03xaQydB+9R7BHPuQENBFOMcBYBCADLMfoA44MwGOB9YT1V4KCy vAfd7E0BTfaAurbG+Olacciz3yd09QOmejFZC6AnoykydyvTFLAWYcSCdISMr88COmmCbJzn sHAogjexXiif6ANUUlHpjxlHCCcELmZUzomNDnEOTxZFeWMTFF9Rf2k2F0Tl4E5kmsNGgtSa aMO0rNZoOEiD/7UfPP3dfh8JCQ1VtUUsQtT1sxos8Eb/HmriJhnaTZ7Hp3jtgTVkV0ybpgFg w6WMaRkrBh17mV0z2ajjmabB7SJxcouSkR0hcpNl4oM74d2/VqoW4BxxxOD1FcNCObCELfIS auZx+XT6s+CE7Qi/c44ibBMR7hyjdzWbABEBAAGJAR8EGAECAAkFAlOMcBYCGwwACgkQsN6d 1ii/Ey9D+Af/WFr3q+bg/8v5tCknCtn92d5lyYTBNt7xgWzDZX8G6/pngzKyWfedArllp0Pn fgIXtMNV+3t8Li1Tg843EXkP7+2+CQ98MB8XvvPLYAfW8nNDV85TyVgWlldNcgdv7nn1Sq8g HwB2BHdIAkYce3hEoDQXt/mKlgEGsLpzJcnLKimtPXQQy9TxUaLBe9PInPd+Ohix0XOlY+Uk QFEx50Ki3rSDl2Zt2tnkNYKUCvTJq7jvOlaPd6d/W0tZqpyy7KVay+K4aMobDsodB3dvEAs6 ScCnh03dDAFgIq5nsB11j3KPKdVoPlfucX2c7kGNH+LUMbzqV6beIENfNexkOfxHf4kBrQQY AQgAIBYhBIUSZ3Lo9gSUpdCX97DendYovxMvBQJa3fDQAhsCAIEJELDendYovxMvdiAEGRYI AB0WIQRTLbB6QfY48x44uB6AXGG7T9hjvgUCWt3w0AAKCRCAXGG7T9hjvk2LAP99B/9FenK/ 1lfifxQmsoOrjbZtzCS6OKxPqOLHaY47BgEAqKKn36YAPpbk09d2GTVetoQJwiylx/Z9/mQI CUbQMg1pNQf9EjA1bNcMbnzJCgt0P9Q9wWCLwZa01SnQWFz8Z4HEaKldie+5bHBL5CzVBrLv 81tqX+/j95llpazzCXZW2sdNL3r8gXqrajSox7LR2rYDGdltAhQuISd2BHrbkQVEWD4hs7iV 1KQHe2uwXbKlguKPhk5ubZxqwsg/uIHw0qZDk+d0vxjTtO2JD5Jv/CeDgaBX4Emgp0NYs8IC UIyKXBtnzwiNv4cX9qKlz2Gyq9b+GdcLYZqMlIBjdCz0yJvgeb3WPNsCOanvbjelDhskx9gd 6YUUFFqgsLtrKpCNyy203a58g2WosU9k9H+LcheS37Ph2vMVTISMszW9W8gyORSgmw==
  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Robert VanVossen <robert.vanvossen@xxxxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Josh Whitehead <josh.whitehead@xxxxxxxxxxxxxxx>, Meng Xu <mengxu@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
  • Delivery-date: Mon, 01 Apr 2019 06:06:56 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 30/03/2019 11:24, Juergen Gross wrote:
> On 29/03/2019 19:42, Andrew Cooper wrote:
>> On 29/03/2019 15:08, Juergen Gross wrote:
>>> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
>>> index 6b5d454630..d1a958143a 100644
>>> --- a/xen/common/schedule.c
>>> +++ b/xen/common/schedule.c
>>> @@ -256,6 +256,7 @@ static void sched_spin_unlock_double(spinlock_t *lock1, 
>>> spinlock_t *lock2,
>>>  int sched_init_vcpu(struct vcpu *v, unsigned int processor)
>>>  {
>>>      struct domain *d = v->domain;
>>> +    struct sched_item item = { .vcpu = v };
>>>  
>>>      v->processor = processor;
>>>  
>>> @@ -267,7 +268,7 @@ int sched_init_vcpu(struct vcpu *v, unsigned int 
>>> processor)
>>>      init_timer(&v->poll_timer, poll_timer_fn,
>>>                 v, v->processor);
>>>  
>>> -    v->sched_priv = SCHED_OP(dom_scheduler(d), alloc_vdata, v,
>>> +    v->sched_priv = SCHED_OP(dom_scheduler(d), alloc_vdata, &item,
>>>                       d->sched_priv);
>>
>> I realise this is perhaps an over-the-top request, but can we see about
>> doing more here?
>>
>> SCHED_OP() is a thoroughly objectionable piece of obfuscation, which
>> breaks cscope/ctags and also results in especially poor code generation.
>>
>> Given that we are changing the interface anyway and touching all
>> codepaths, would you mind also adding static inline wrappers like I
>> started with 340edc3 ?
> 
> Okay, I'll do that.
> 
>> TBH, I'm even happy to give this a go and give you the back the
>> resulting tree, if you'd prefer.
> 
> I think its is easier to do it myself, as I'm touching nearly all of
> the call sites anyway.

And another thought I had: with RETPOLINE indirect jumps are even more
expensive. Would it be a good idea to remove the function pointers from
struct scheduler and generate the inline wrappers at build time? The
wrappers could then call the related specific scheduler function based
on the scheduler Id using a chain of if ... else if ... statements. It
would prefer the default scheduler over the others and test only for
configured schedulers. Scheduler registration could be done the same way
removing the need for an extra link section.


Juergen

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