• Len Brown's avatar
    x86/smpboot: Remove SIPI delays from cpu_up() · a9bcaa02
    Len Brown authored
    MPS 1.4 example code shows the following required delays during processor
    on-lining:
    
    	INIT
    	 udelay(10,000)
    	SIPI
    	 udelay(200)
    	SIPI
    	 udelay(200) /* Linux actually implements this as udelay(300) */
    
    Linux skips the udelay(10,000) on modern processors.
    This patch removes the udelay(200) after each SIPI
    on those same processors.
    
    All three legacy delays can be restored by the cmdline
    "cpu_init_udelay=10000".
    
    As measured by analyze_suspend.py, this patch speeds
    processor resume time on my desktop from 2.4ms to 1.8ms, per AP.
    Signed-off-by: default avatarLen Brown <len.brown@intel.com>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Igor Mammedov <imammedo@redhat.com>
    Cc: Jan H. Schönherr <jschoenh@amazon.de>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
    Link: http://lkml.kernel.org/r/a5dfdbc8fbfdd813784da204aad5677fe459ac37.1439739165.git.len.brown@intel.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    a9bcaa02
smpboot.c 37.2 KB