• Mathieu Desnoyers's avatar
    membarrier: Provide register expedited private command · a961e409
    Mathieu Desnoyers authored
    This introduces a "register private expedited" membarrier command which
    allows eventual removal of important memory barrier constraints on the
    scheduler fast-paths. It changes how the "private expedited" membarrier
    command (new to 4.14) is used from user-space.
    
    This new command allows processes to register their intent to use the
    private expedited command.  This affects how the expedited private
    command introduced in 4.14-rc is meant to be used, and should be merged
    before 4.14 final.
    
    Processes are now required to register before using
    MEMBARRIER_CMD_PRIVATE_EXPEDITED, otherwise that command returns EPERM.
    
    This fixes a problem that arose when designing requested extensions to
    sys_membarrier() to allow JITs to efficiently flush old code from
    instruction caches.  Several potential algorithms are much less painful
    if the user register intent to use this functionality early on, for
    example, before the process spawns the second thread.  Registering at
    this time removes the need to interrupt each and every thread in that
    process at the first expedited sys_membarrier() system call.
    Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    a961e409
exec.c 45.8 KB