linux-kernel - Re: x86, perf: throttling issues with long nmi latencies

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Message-ID: <20131015143931.GN10651@twins.programming.kicks-ass.net>
Date:	Tue, 15 Oct 2013 16:39:31 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	dave.hansen@...ux.intel.com, eranian@...gle.com,
	ak@...ux.intel.com, jmario@...hat.com,
	linux-kernel@...r.kernel.org, acme@...radead.org
Subject: Re: x86, perf: throttling issues with long nmi latencies

On Tue, Oct 15, 2013 at 10:36:31AM -0400, Don Zickus wrote:
> > > +refill:
> > > +	if (kernel_ip(ip)) {
> > > +		u8 *buf = &__get_cpu_var(insn_page[0]);
> > > +		size = PAGE_SIZE - ((unsigned long)to & (PAGE_SIZE-1));
> > > +		if (size < MAX_INSN_SIZE) {
> > > +			/*
> > > +			 * If we're going to have to touch two pages; just copy
> > > +			 * as much as we can hold.
> > > +			 */
> > > +			size = PAGE_SIZE;

> Quick thoughts?

Yeah, see the patch I just send; but notably I got the kernel_ip(ip)
case the wrong way about. See how it copies userspace memory for kernel
IPs and vice versa.


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