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Re: [Xen-devel] [PATCH 54/60] xen/sched: add minimalistic idle scheduler for free cpus
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Tue, 28 May 2019 13:58:45 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, WeiLiu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Tue, 28 May 2019 11:58:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 28/05/2019 13:47, Jan Beulich wrote:
>>>> On 28.05.19 at 12:33, <jgross@xxxxxxxx> wrote:
>> Instead of having a full blown scheduler running for the free cpus
>> add a very minimalistic scheduler for that purpose only ever scheduling
>> the related idle vcpu. This has the big advantage of not needing any
>> per-cpu, per-domain or per-scheduling unit data for free cpus and in
>> turn simplifying moving cpus to and from cpupools a lot.
>
> And the null scheduler is not minimalistic enough?
The main disadvantage of the null scheduler are the need for private
data (which has to be allocated/freed on scheduler switch), its not
yet perfect stability, and its "complexity" (e.g. 900 lines vs. 50).
>
>> --- a/xen/arch/arm/smpboot.c
>> +++ b/xen/arch/arm/smpboot.c
>> @@ -350,8 +350,6 @@ void start_secondary(unsigned long boot_phys_offset,
>>
>> setup_cpu_sibling_map(cpuid);
>>
>> - scheduler_percpu_init(cpuid);
>> -
>> /* Run local notifiers */
>> notify_cpu_starting(cpuid);
>> /*
>> --- a/xen/arch/x86/smpboot.c
>> +++ b/xen/arch/x86/smpboot.c
>> @@ -382,8 +382,6 @@ void start_secondary(void *unused)
>>
>> set_cpu_sibling_map(cpu);
>>
>> - scheduler_percpu_init(cpu);
>> -
>> init_percpu_time();
>>
>> setup_secondary_APIC_clock();
>
> Seeing you revert here what an earlier patch in the series has added,
> I don't suppose re-ordering could avoid this code churn?
This would require another major shuffling of patches. I'd like to avoid
that.
Juergen
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