Re: [Patch v4 07/16] x86, irq: Prefer assigned ID in APIC ID register for x86_64

From: Thomas Gleixner <tglx@linutronix.de>
To: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Yinghai Lu <yinghai@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Grant Likely <grant.likely@linaro.org>,
	x86@kernel.org, Prarit Bhargava <prarit@redhat.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tony Luck <tony.luck@intel.com>, Joerg Roedel <joro@8bytes.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-acpi@vger.kernel.org,
	Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [Patch v4 07/16] x86, irq: Prefer assigned ID in APIC ID register for x86_64
Date: Tue, 9 Sep 2014 13:04:51 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.10.1409091256270.11037@nanos> (raw)
In-Reply-To: <1409192561-19744-8-git-send-email-jiang.liu@linux.intel.com>

On Thu, 28 Aug 2014, Jiang Liu wrote:

> From: Yinghai Lu <yinghai@kernel.org>
> 
> Perfer the assigned ID in APIC ID register for x86_64 if it's still
> available.
> 
> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
> Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
> ---
>  arch/x86/kernel/apic/io_apic.c |   38 +++++++++++++++++++++++++++++++++-----
>  1 file changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index 3faf9599ff29..196d9c15fdec 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -3575,26 +3575,54 @@ static int __init io_apic_get_unique_id(int ioapic, int apic_id)
>  	return apic_id;
>  }
>  
> -static u8 __init io_apic_unique_id(u8 id)
> +static u8 io_apic_unique_id(int idx, u8 id)

How is that change related to the changelog?

>  {
>  	if ((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) &&
>  	    !APIC_XAPIC(apic_version[boot_cpu_physical_apicid]))
> -		return io_apic_get_unique_id(nr_ioapics, id);
> +		return io_apic_get_unique_id(idx, id);
>  	else
>  		return id;
>  }
>  #else
> -static u8 __init io_apic_unique_id(u8 id)
> +static u8 io_apic_unique_id(int idx, u8 id)
>  {
>  	int i;
> +	u8 new_id;
> +	unsigned long flags;
>  	DECLARE_BITMAP(used, 256);
> +	union IO_APIC_reg_00 reg_00;
>  
>  	bitmap_zero(used, 256);
>  	for_each_ioapic(i)
>  		__set_bit(mpc_ioapic_id(i), used);
>  	if (!test_bit(id, used))
>  		return id;
> -	return find_first_zero_bit(used, 256);
> +
> +	/* check register at first */
> +	raw_spin_lock_irqsave(&ioapic_lock, flags);
> +	reg_00.raw = io_apic_read(idx, 0);
> +	raw_spin_unlock_irqrestore(&ioapic_lock, flags);
> +	new_id = reg_00.bits.ID;
> +	if (!test_bit(new_id, used)) {
> +		apic_printk(APIC_VERBOSE, KERN_INFO
> +			"IOAPIC[%d]: Using reg apic_id %d instead of %d\n",
> +			 idx, new_id, id);
> +		return new_id;
> +	}
> +
> +	new_id = find_first_zero_bit(used, 256);
> +	reg_00.bits.ID = new_id;
> +	raw_spin_lock_irqsave(&ioapic_lock, flags);
> +	io_apic_write(idx, 0, reg_00.raw);
> +	reg_00.raw = io_apic_read(idx, 0);
> +	raw_spin_unlock_irqrestore(&ioapic_lock, flags);
> +
> +	/* Sanity check */
> +	if (reg_00.bits.ID != new_id)
> +		pr_warn("IOAPIC[%d]: Unable to change apic_id to %d!\n",
> +			idx, new_id);

So we detect, that the ID could not be changed and we return it
nevertheless?

Thanks,

	tglx