linux-kernel - Re: [RFC 2/2] perf: Marker software event and ioctl

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Date:	Fri, 12 Sep 2014 10:00:09 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	Pawel Moll <pawel.moll@....com>
CC:	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [RFC 2/2] perf: Marker software event and ioctl

On 09/12/2014 08:57 AM, Pawel Moll wrote:
> On Fri, 2014-09-12 at 13:43 +0100, Christopher Covington wrote:
>> Just to ask the dumb questions in case the answers I've come up with are
>> wrong: What is PAGE_SIZE on an arm64 kernel? 
> 
> It's either 4 or 64k, depending on CONFIG_ARM64_64K_PAGES.
> 
>> How does userspace know?
>>
> #include <unistd.h>
> #include <stdio.h>
> 
> int main(void)
> {
> 	printf("%ld\n", sysconf(_SC_PAGESIZE));
> 	return 0;
> }

Oh excellent, that actually works. Based on a misreading of the glibc code I
thought it was hard-coded to 64K.

Thanks,
Christopher

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