• Andy Lutomirski's avatar
    x86/fpu: Default eagerfpu=on on all CPUs · 58122bf1
    Andy Lutomirski authored
    We have eager and lazy FPU modes, introduced in:
    
      304bceda ("x86, fpu: use non-lazy fpu restore for processors supporting xsave")
    
    The result is rather messy.  There are two code paths in almost all
    of the FPU code, and only one of them (the eager case) is tested
    frequently, since most kernel developers have new enough hardware
    that we use eagerfpu.
    
    It seems that, on any remotely recent hardware, eagerfpu is a win:
    glibc uses SSE2, so laziness is probably overoptimistic, and, in any
    case, manipulating TS is far slower that saving and restoring the
    full state.  (Stores to CR0.TS are serializing and are poorly
    optimized.)
    
    To try to shake out any latent issues on old hardware, this changes
    the default to eager on all CPUs.  If no performance or functionality
    problems show up, a subsequent patch could remove lazy mode entirely.
    Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Fenghua Yu <fenghua.yu@intel.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: yu-cheng yu <yu-cheng.yu@intel.com>
    Link: http://lkml.kernel.org/r/ac290de61bf08d9cfc2664a4f5080257ffc1075a.1453675014.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    58122bf1
init.c 11.1 KB