linux-kernel - Re: [patch] genapic: default to physical mode on hotplug CPU kernels

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20061128143145.B16460@unix-os.sc.intel.com>
Date:	Tue, 28 Nov 2006 14:31:46 -0800
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	mm-commits@...r.kernel.org, ak@...e.de, ashok.raj@...el.com,
	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] genapic: default to physical mode on hotplug CPU kernels

On Tue, Nov 28, 2006 at 09:23:22PM +0100, Ingo Molnar wrote:
> 
> * Siddha, Suresh B <suresh.b.siddha@...el.com> wrote:
> 
> > On Tue, Nov 28, 2006 at 07:33:46AM +0100, Ingo Molnar wrote:
> > > -	if (clusters <= 1 && max_cluster <= 8 && cluster_cnt[0] == max_cluster)
> > > +	if (max_apic < 8)
> > 
> > Patch mostly looks good.  Instead of checking for max_apic, can we use
> > 	cpus_weight(cpu_possible_map) <= 8
> 
> ok - but i think it's still possible the BIOS tells us APIC IDs that are 
> larger than 7, even if there are fewer CPUs. So i think the patch below 
> should cover it. Agreed?
> 

I think it is ok to use flat mode even when APIC IDs are larger than 7, as
we rely on LDR's which are programmed using smp_processor_id().

IMO, cpus_weight check should be fine.

thanks,
suresh

> 	Ingo
> 
> -------------------->
> From: Ingo Molnar <mingo@...e.hu>
> Subject: [patch] genapic: default to physical mode on hotplug CPU kernels
> 
> default to physical mode on hotplug CPU kernels.
> 
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> Index: linux/arch/x86_64/kernel/genapic.c
> ===================================================================
> --- linux.orig/arch/x86_64/kernel/genapic.c
> +++ linux/arch/x86_64/kernel/genapic.c
> @@ -51,7 +51,7 @@ void __init clustered_apic_check(void)
>  			max_apic = id;
>  	}
>  
> -	if (max_apic < 8)
> +	if (max_apic < 8 && cpus_weight(cpu_possible_map) <= 8)
>  		genapic = &apic_flat;
>  	else
>  		genapic = &apic_physflat;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/