linux-kernel - Re: [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single

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Message-ID: <87mv7gytmk.fsf@yhuang-dev.intel.com>
Date:   Fri, 04 Aug 2017 10:05:55 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     "Huang\, Ying" <ying.huang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>, Aaron Lu <aaron.lu@...el.com>
Subject: Re: [PATCH 3/3] IPI: Avoid to use 2 cache lines for one call_single_data

"Huang, Ying" <ying.huang@...el.com> writes:

> Peter Zijlstra <peterz@...radead.org> writes:
> [snip]
>> diff --git a/include/linux/smp.h b/include/linux/smp.h
>> index 68123c1fe549..8d817cb80a38 100644
>> --- a/include/linux/smp.h
>> +++ b/include/linux/smp.h
>> @@ -14,13 +14,16 @@
>>  #include <linux/llist.h>
>>  
>>  typedef void (*smp_call_func_t)(void *info);
>> -struct call_single_data {
>> +struct __call_single_data {
>>  	struct llist_node llist;
>>  	smp_call_func_t func;
>>  	void *info;
>>  	unsigned int flags;
>>  };
>>  
>> +typedef struct __call_single_data call_single_data_t
>> +	__aligned(sizeof(struct __call_single_data));
>> +
>
> Another requirement of the alignment is that it should be the power of
> 2.  Otherwise, for example, if someone adds a field to struct, so that
> the size becomes 40 on x86_64.  The alignment should be 64 instead of
> 40.

Thanks Aaron, he reminded me that there is a roundup_pow_of_two().  So
the typedef could be,

typedef struct __call_single_data call_single_data_t
	__aligned(roundup_pow_of_two(sizeof(struct __call_single_data));

Best Regards,
Huang, Ying

> Best Regards,
> Huang, Ying
>
>>  /* total number of cpus in this system (may exceed NR_CPUS) */
>>  extern unsigned int total_cpus;
>>  
> [snip]