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    SubjectRe: [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.


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