linux-kernel - Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

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Date:	Tue, 20 Mar 2007 17:14:45 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Matt Mackall <mpm@...enic.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@....de>,
	David Miller <davem@...emloft.net>, mingo@...e.hu,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	chrisw@...s-sol.org, anthony@...emonkey.ws, netdev@...r.kernel.org
Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops
 callsites to make them patchable

Jeremy Fitzhardinge wrote:
> Zachary Amsden wrote:
>   
>> I think Jeremy's idea was to have interrupt handlers leave interrupts
>> disabled on exit if pda.intr_mask was set.  In which case, they would
>> bypass all work and we could never get preempted.
>>     
>
> Yes, I was worried that if we left the isr without actually handling the
> interrupt, it would still be asserted and we'd just get interrupted
> again.  The idea is that we avoid touching cli/sti for the common case
> of no interrupts while interrupts are disabled, but we'd still need to
> fall back to using them if an interrupt becomes pending.
>
>   
>> I don't think leaving hardware interrupts disabled for such a long
>> time is good though. 
>>     
>
> How long?  It would be no longer than now, and possibly less, wouldn't it?
>   

Hmm.  Perhaps.  Something about the asymmetry bothers me alot though.

Zach

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