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Subject: Re: [Patch v3 1/3] lib: Restrict cpumask_local_spread to houskeeping
 CPUs
To:     Andrew Morton <akpm@linux-foundation.org>,
        Nitesh Narayan Lal <nitesh@redhat.com>
CC:     <linux-kernel@vger.kernel.org>, <linux-api@vger.kernel.org>,
        <frederic@kernel.org>, <mtosatti@redhat.com>,
        <juri.lelli@redhat.com>, <abelits@marvell.com>,
        <bhelgaas@google.com>, <linux-pci@vger.kernel.org>,
        <rostedt@goodmis.org>, <mingo@kernel.org>, <peterz@infradead.org>,
        <tglx@linutronix.de>, <davem@davemloft.net>,
        <sfr@canb.auug.org.au>, <stephen@networkplumber.org>,
        <rppt@linux.vnet.ibm.com>, yuqi jin <jinyuqi@huawei.com>
References: <20200623192331.215557-1-nitesh@redhat.com>
 <20200623192331.215557-2-nitesh@redhat.com>
 <20200624122647.766bec7760d9197ba71a58c4@linux-foundation.org>
From:   Shaokun Zhang <zhangshaokun@hisilicon.com>
Message-ID: <e6c261a1-1fec-3faf-c49c-51a88a7f521c@hisilicon.com>
Date:   Mon, 29 Jun 2020 17:01:41 +0800
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Hi Andrew,

?? 2020/6/25 3:26, Andrew Morton д??:
> On Tue, 23 Jun 2020 15:23:29 -0400 Nitesh Narayan Lal <nitesh@redhat.com> wrote:
> 
>> From: Alex Belits <abelits@marvell.com>
>>
>> The current implementation of cpumask_local_spread() does not respect the
>> isolated CPUs, i.e., even if a CPU has been isolated for Real-Time task,
>> it will return it to the caller for pinning of its IRQ threads. Having
>> these unwanted IRQ threads on an isolated CPU adds up to a latency
>> overhead.
>>
>> Restrict the CPUs that are returned for spreading IRQs only to the
>> available housekeeping CPUs.
>>
>> ...
>>
>> --- a/lib/cpumask.c
>> +++ b/lib/cpumask.c
>> @@ -6,6 +6,7 @@
>>  #include <linux/export.h>
>>  #include <linux/memblock.h>
>>  #include <linux/numa.h>
>> +#include <linux/sched/isolation.h>
>>  
>>  /**
>>   * cpumask_next - get the next cpu in a cpumask
>> @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
>>   */
>>  unsigned int cpumask_local_spread(unsigned int i, int node)
>>  {
>> -	int cpu;
>> +	int cpu, hk_flags;
>> +	const struct cpumask *mask;
>>  
>> +	hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ;
>> +	mask = housekeeping_cpumask(hk_flags);
>>  	/* Wrap: we always want a cpu. */
>> -	i %= num_online_cpus();
>> +	i %= cpumask_weight(mask);
>>  
>>  	if (node == NUMA_NO_NODE) {
>> -		for_each_cpu(cpu, cpu_online_mask)
>> +		for_each_cpu(cpu, mask) {
>>  			if (i-- == 0)
>>  				return cpu;
>> +		}
>>  	} else {
>>  		/* NUMA first. */
>> -		for_each_cpu_and(cpu, cpumask_of_node(node), cpu_online_mask)
>> +		for_each_cpu_and(cpu, cpumask_of_node(node), mask) {
>>  			if (i-- == 0)
>>  				return cpu;
>> +		}
>>  
>> -		for_each_cpu(cpu, cpu_online_mask) {
>> +		for_each_cpu(cpu, mask) {
>>  			/* Skip NUMA nodes, done above. */
>>  			if (cpumask_test_cpu(cpu, cpumask_of_node(node)))
>>  				continue;
> 
> Are you aware of these changes to cpu_local_spread()?
> https://lore.kernel.org/lkml/1582768688-2314-1-git-send-email-zhangshaokun@hisilicon.com/
> 
> I don't see a lot of overlap but it would be nice for you folks to

Yeah, it's a different issue from Nitesh. About our's patch, it has been
linux-next long time, will it be merged in Linus's tree?

Thanks,
Shaokun

> check each other's homework ;)
> 
> 
> 
> .
>