• Milton Miller's avatar
    powerpc: Consolidate ipi message mux and demux · 23d72bfd
    Milton Miller authored
    Consolidate the mux and demux of ipi messages into smp.c and call
    a new smp_ops callback to actually trigger the ipi.
    
    The powerpc architecture code is optimised for having 4 distinct
    ipi triggers, which are mapped to 4 distinct messages (ipi many, ipi
    single, scheduler ipi, and enter debugger).  However, several interrupt
    controllers only provide a single software triggered interrupt that
    can be delivered to each cpu.  To resolve this limitation, each smp_ops
    implementation created a per-cpu variable that is manipulated with atomic
    bitops.  Since these lines will be contended they are optimialy marked as
    shared_aligned and take a full cache line for each cpu.  Distro kernels
    may have 2 or 3 of these in their config, each taking per-cpu space
    even though at most one will be in use.
    
    This consolidation removes smp_message_recv and replaces the single call
    actions cases with direct calls from the common message recognition loop.
    The complicated debugger ipi case with its muxed crash handling code is
    moved to debug_ipi_action which is now called from the demux code (instead
    of the multi-message action calling smp_message_recv).
    
    I put a call to reschedule_action to increase the likelyhood of correctly
    merging the anticipated scheduler_ipi() hook coming from the scheduler
    tree; that single required call can be inlined later.
    
    The actual message decode is a copy of the old pseries xics code with its
    memory barriers and cache line spacing, augmented with a per-cpu unsigned
    long based on the book-e doorbell code.  The optional data is set via a
    callback from the implementation and is passed to the new cause-ipi hook
    along with the logical cpu number.  While currently only the doorbell
    implemntation uses this data it should be almost zero cost to retrieve and
    pass it -- it adds a single register load for the argument from the same
    cache line to which we just completed a store and the register is dead
    on return from the call.  I extended the data element from unsigned int
    to unsigned long in case some other code wanted to associate a pointer.
    
    The doorbell check_self is replaced by a call to smp_muxed_ipi_resend,
    conditioned on the CPU_DBELL feature.  The ifdef guard could be relaxed
    to CONFIG_SMP but I left it with BOOKE for now.
    
    Also, the doorbell interrupt vector for book-e was not calling irq_enter
    and irq_exit, which throws off cpu accounting and causes code to not
    realize it is running in interrupt context.  Add the missing calls.
    Signed-off-by: default avatarMilton Miller <miltonm@bga.com>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    23d72bfd
smp.c 6.26 KB