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    SubjectRe: [PATCH v6] Unified trace buffer

    On Fri, 26 Sep 2008, Martin Bligh wrote:

    > On Fri, Sep 26, 2008 at 11:59 AM, Peter Zijlstra <peterz@infradead.org> wrote:
    > > On Fri, 2008-09-26 at 14:05 -0400, Steven Rostedt wrote:
    > >
    > >> +struct buffer_page {
    > >> + u64 time_stamp;
    > >> + unsigned char body[];
    > >> +};
    > >> +
    > >> +#define BUF_PAGE_SIZE (PAGE_SIZE - sizeof(u64))
    > >
    > > Since you're already using the page frame, you can stick this per page
    > > timestamp in there as well, and get the full page for data.
    > >
    > > You can either use a struct page overlay like slob does, or add a u64 in
    > > the union that contains struct {private, mapping}.
    >
    > What did you guys think of Mathieu's idea of sticking the buffer length
    > in the header here, rather than using padding events? Seemed cleaner
    > to me.

    Actually I like the padding. This way when I move the event pointer
    forward, I only need to compare it to a constant (PAGE_SIZE), or test to
    see if the event is padding. Placing this into the buffer page, I will
    have to always compare it to that pointer.

    But I guess I could change it to that if needed. That doesn't affect the
    API, as it is only internal.

    I'm almost done with v7, perhaps I might try that with v8 to see if I like
    it better.

    -- Steve



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