linux-kernel - Re: [PATCH] x86/hyperv: LP creation with lp

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Message-ID: <572da60e-714f-b207-a89e-6dc40209e2da@linux.microsoft.com>
Date:   Mon, 31 May 2021 16:31:04 +0530
From:   Praveen Kumar <kumarpraveen@...ux.microsoft.com>
To:     Wei Liu <wei.liu@...nel.org>
Cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, nunodasneves@...ux.microsoft.com,
        viremana@...ux.microsoft.com, sunilmut@...rosoft.com,
        Michael Kelley <mikelley@...rosoft.com>
Subject: Re: [PATCH] x86/hyperv: LP creation with lp_index on same CPU-id



On 5/31/2021 4:27 PM, Wei Liu wrote:
> On Mon, May 31, 2021 at 01:10:46PM +0530, Praveen Kumar wrote:
>> The hypervisor expects the lp_index to be same as cpu-id during LP creation
>> This fix correct the same, as cpu_physical_id can give different cpu-id.
> 
> Code looks fine to me, but the commit message can be made clearer.
> 
> """
> The hypervisor expects the logical processor index to be the same as
> CPU's id during logical processor creation. Using cpu_physical_id
> confuses Microsoft Hypervisor's scheduler. That causes the root
> partition not boot when core scheduler is used.
> 
> This patch removes the call to cpu_physical_id and uses the CPU index
> directly for bringing up logical processor. This scheme works for both
> classic scheduler and core scheduler.
> 
> Fixes: 333abaf5abb3 (x86/hyperv: implement and use hv_smp_prepare_cpus)
> """
> 
> No action is required from you. If you are fine with this commit message
> I can incorporate it and update the subject line when committing this
> patch.
> 

Thanks Wei for your comments. I'm fine with your inputs. Please go ahead. Thanks.

Regards,

~Praveen.

>>
>> Signed-off-by: Praveen Kumar <kumarpraveen@...ux.microsoft.com>
>> ---
>>  arch/x86/kernel/cpu/mshyperv.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
>> index 22f13343b5da..4fa0a4280895 100644
>> --- a/arch/x86/kernel/cpu/mshyperv.c
>> +++ b/arch/x86/kernel/cpu/mshyperv.c
>> @@ -236,7 +236,7 @@ static void __init hv_smp_prepare_cpus(unsigned int max_cpus)
>>  	for_each_present_cpu(i) {
>>  		if (i == 0)
>>  			continue;
>> -		ret = hv_call_add_logical_proc(numa_cpu_node(i), i, cpu_physical_id(i));
>> +		ret = hv_call_add_logical_proc(numa_cpu_node(i), i, i);
>>  		BUG_ON(ret);
>>  	}
>>  
>> -- 
>> 2.25.1
>>