linux-kernel - Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry

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Date:	Fri, 1 May 2015 19:59:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, williams@...hat.com,
	Andrew Lutomirski <luto@...nel.org>, fweisbec@...hat.com,
	Peter Zijlstra <peterz@...radead.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable
 & enable from context tracking on syscall entry


* Rik van Riel <riel@...hat.com> wrote:

> > I.e. much of what we do today, except that we could skip variable 
> > work such as the scheduler tick or (unforced) RCU processing like 
> > the RCU softirq work.
> 
> Any ideas how we could avoid that sampling timer interrupt latency 
> stacking up when dealing with both guest and host?

Well, it would be host_latency+guest_latency worst-case, right?

That should still be bounded, as long as both guest and host is 
running nohz-full mode.

Also, technically when the host gets such an IRQ, the guest is 
interrupted as well. So the host could do the guest's work and pass 
through the result via paravirt or so.

Thanks,

	Ingo
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