RE: [kvm-devel] [02/17][PATCH] Implement smp_call_function_mask foria64 - V8

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

Jes Sorensen wrote:
> Zhang, Xiantao wrote:
>>> From 697d50286088e98da5ac8653c80aaa96c81abf87 Mon Sep 17 00:00:00
>>> 2001 
>> From: Xiantao Zhang <xiantao.zhang@xxxxxxxxx>
>> Date: Mon, 31 Mar 2008 09:50:24 +0800
>> Subject: [PATCH] KVM:IA64: Implement smp_call_function_mask for ia64
>> 
>> This function provides more flexible interface for smp
>> infrastructure. Signed-off-by: Xiantao Zhang
>> <xiantao.zhang@xxxxxxxxx> 
> 
> Hi Xiantao,
> 
> I'm a little wary of the performance impact of this change. Doing a
> cpumask compare on all smp_call_function calls seems a little
> expensive. Maybe it's just noise in the big picture compared to the
> actual cost of the IPIs, but I thought I'd bring it up.
> Keep in mind that a cpumask can be fairly big these days, max NR_CPUS
> is currently 4096. For those booting a kernel with NR_CPUS at 4096 on
> a dual CPU machine, it would be a bit expensive.
> 
> Why not keep smp_call_function() the way it was before, rather than
> implementing it via the call to smp_call_function_mask()?

Hi, Jes
   I'm not aware of the performance impact before.  If the worst case
occurs,  it need 64 comparisions ?  Maybe keeping old smp_call_function
is better ? 
Xiantao
> 
>
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