linux-kernel - Re: [PATCH] x86_64: Restore the proper NR

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Message-ID: <4895561C.2030004@goop.org>
Date:	Sat, 02 Aug 2008 23:54:20 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Yinghai Lu <yhlu.kernel@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: Restore the proper NR_IRQS define so larger systems
 work.

Eric W. Biederman wrote:
> Xen pv 64 will work at least as well with a larger definition for
> NR_IRQS as it will work with a smaller definition, and since
> NR_VECTORS is 256 we always have more irqs with the 32bit definition
> we were mistakenly using. 
>
> Xen has 1024 event channels so I expect 1024 would the nice number to
> provide there.
>   

Yes, but really its overkill.  It needs about 6 interrupts/cpu for 
normal system overhead (timer, IPI, things like that), and then some 
amount for virtual devices.

dom0 - the control domain - will need some number of events per other 
guest domain, so it can start feeling the pressure depending on how many 
domains and devices there are.

    J
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