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Date: Wed, 19 Feb 2014 14:02:36 -0800
From: Dave Hansen <dave.hansen@intel.com>
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To: Peter Zijlstra <peterz@infradead.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>
CC: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Mike Galbraith <efault@gmx.de>, Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>, Andi Kleen <ak@linux.intel.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Matt Fleming <matt.fleming@intel.com>
Subject: Re: [PATCH v1 03/11] perf: Allow for multiple ring buffers per event
References: <1391683834-29868-1-git-send-email-alexander.shishkin@linux.intel.com> <1391683834-29868-4-git-send-email-alexander.shishkin@linux.intel.com> <20140217143340.GR27965@twins.programming.kicks-ass.net>
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On 02/17/2014 06:33 AM, Peter Zijlstra wrote:
> Then write the PERF_RECORD_DATA structure into the normal ring-buffer
> location; set data_offset to point to the first page boundary, data_size
> to 1mb.
> 
> Then frob things such that perf_mmap_to_page() for the next 1mb of pages
> points to your buffer pages and wipe the page-table entries.

Wouldn't we have to teach a ton of code how to be IRQ safe for this to
work?  Just step one: how do we go modifying page tables safely from an
interrupt?  mm->page_table_lock is a plain non-irq spinlock.