linux-kernel - Re: [PATCH 3/3] v4: Add support for Numascale's NumaChip

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Message-ID: <4EDC938D.6000304@numascale.com>
Date:	Mon, 05 Dec 2011 10:49:01 +0100
From:	Steffen Persvold <sp@...ascale.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Daniel J Blueman <daniel@...ascale-asia.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 3/3] v4: Add support for Numascale's NumaChip

On 12/5/2011 10:10, Ingo Molnar wrote:
[]
>
> The patches are now structured mostly right and look clean.

Thanks for the review!

>
> Other small details i noticed:
>
>> +static int numachip_system;
>> +
>> +static struct apic apic_numachip;
>
> Those want to be __read_mostly - this also makes them more NUMA
> friendly .

Ok, makes sense.

>
>> +static int __cpuinit numachip_wakeup_secondary(int phys_apicid, unsigned long start_rip)
>> +{
>> +#ifdef CONFIG_SMP
>> +	union numachip_csr_g3_ext_irq_gen int_gen;
>> +	unsigned long flags;
>> +
>> +	int_gen.s._destination_apic_id = phys_apicid;
>> +	int_gen.s._vector = 0;
>> +	int_gen.s._msgtype = APIC_DM_INIT>>  8;
>> +	int_gen.s._index = 0;
>> +
>> +	local_irq_save(flags);
>> +	write_lcsr(CSR_G3_EXT_IRQ_GEN, int_gen.v);
>> +	local_irq_restore(flags);
>> +
>> +	mdelay(10);
>
> Exactly why does it have to sleep 10 milliseconds here? Please
> document it.

It doesn't. I'm not quite sure why it was left in there.. We will remove 
it. Thanks for catching it.

>
>> +
>> +	int_gen.s._msgtype = APIC_DM_STARTUP>>  8;
>> +	int_gen.s._vector = start_rip>>  12;
>> +
>> +	local_irq_save(flags);
>> +	write_lcsr(CSR_G3_EXT_IRQ_GEN, int_gen.v);
>> +	local_irq_restore(flags);
>> +
>> +	atomic_set(&init_deasserted, 1);
>> +#endif
>> +	return 0;
>
> You could do a 'depends on SMP' and stop uglifying the code with
> !SMP considerations. Unless a single-core installation with a UP
> kernel is possible and desired.

Agreed.

>
>> +static void numachip_send_IPI_allbutself(int vector)
>> +{
>> +	unsigned int this_cpu = smp_processor_id();
>> +	unsigned int cpu;
>> +	unsigned long flags;
>> +
>> +	local_irq_save(flags);
>> +	for_each_online_cpu(cpu) {
>> +		if (cpu != this_cpu)
>> +			numachip_send_IPI_one(cpu, vector);
>> +	}
>> +	local_irq_restore(flags);
>> +}
>
> This seems preempt unsafe: you take smp_processor_id() before
> disabling hardirqs.

Hmm, yes. Again some debug stuff laying around, local_irq_save/restore 
isn't really needed there I think.

We will redo this last patch and re-send after testing. Thanks!

Kind regards,
-- 
Steffen Persvold, Chief Architect NumaChip
Numascale AS - www.numascale.com
Tel: +47 92 49 25 54 Skype: spersvold
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