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Date: Fri, 14 Mar 2014 11:41:00 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Dave Hansen <dave.hansen@...el.com> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org, Frederic Weisbecker <fweisbec@...il.com>, Mike Galbraith <efault@....de>, Paul Mackerras <paulus@...ba.org>, Stephane Eranian <eranian@...gle.com>, Andi Kleen <ak@...ux.intel.com>, Adrian Hunter <adrian.hunter@...el.com>, Matt Fleming <matt.fleming@...el.com> Subject: Re: [PATCH v1 03/11] perf: Allow for multiple ring buffers per event On Wed, Feb 19, 2014 at 02:02:36PM -0800, Dave Hansen wrote: > 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. One could modify existing page tables the same way we do the lockless lookup for GUP. But instead of doing the get_page() we do a pte modification. But I suppose we can push all that to task context by having the polling task do it before it gets to userspace again. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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