linux-kernel - Re: [PATCH v3 3/9] x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not

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Date:   Fri, 19 Jul 2019 18:41:11 +0000
From:   Nadav Amit <namit@...are.com>
To:     Dave Hansen <dave.hansen@...el.com>
CC:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v3 3/9] x86/mm/tlb: Open-code on_each_cpu_cond_mask() for
 tlb_is_not_lazy()

> On Jul 19, 2019, at 11:36 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> 
> On 7/18/19 5:58 PM, Nadav Amit wrote:
>> @@ -865,7 +893,7 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
>> 	if (cpumask_test_cpu(cpu, &batch->cpumask)) {
>> 		lockdep_assert_irqs_enabled();
>> 		local_irq_disable();
>> -		flush_tlb_func_local(&full_flush_tlb_info);
>> +		flush_tlb_func_local((void *)&full_flush_tlb_info);
>> 		local_irq_enable();
>> 	}
> 
> This looks like superfluous churn.  Is it?

Unfortunately not, since full_flush_tlb_info is defined as const. Without it
you would get:

warning: passing argument 1 of ‘flush_tlb_func_local’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]

And flush_tlb_func_local() should get (void *) argument since it is also
used by the SMP infrastructure.