• John Hawkes's avatar
    [PATCH] drop note_interrupt() for per-CPU for proper scaling · b60c1f6f
    John Hawkes authored
    The "unhandled interrupts" catcher, note_interrupt(), increments a global
    desc->irq_count and grossly damages scaling of very large systems, e.g.,
    >192p ia64 Altix, because of this highly contented cacheline, especially
    for timer interrupts.  384p is severely crippled, and 512p is unuseable.
    All calls to note_interrupt() can be disabled by booting with "noirqdebug",
    but this disables the useful interrupt checking for all interrupts.
    I propose eliminating note_interrupt() for all per-CPU interrupts.  This
    was the behavior of linux-2.6.10 and earlier, but in 2.6.11 a code
    restructuring added a call to note_interrupt() for per-CPU interrupts.
    Besides, note_interrupt() is a bit racy for concurrent CPU calls anyway, as
    the desc->irq_count++ increment isn't atomic (which, if done, would make
    scaling even worse).
    Signed-off-by: default avatarJohn Hawkes <hawkes@sgi.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
handle.c 4.68 KB