x86/smpboot: Remove SIPI delays from cpu_up()
authorLen Brown <len.brown@intel.com>
Sun, 16 Aug 2015 15:45:47 +0000 (11:45 -0400)
committerIngo Molnar <mingo@kernel.org>
Mon, 17 Aug 2015 08:42:27 +0000 (10:42 +0200)
commita9bcaa02a5104ace6a9d9e4a9cd9192a9e7744d6
tree6ef02ae00a81bf4afe1df91defc2ad6b1665a122
parent2d99af8e8fd6c2dea11ab539f7aba69c37b845b4
x86/smpboot: Remove SIPI delays from cpu_up()

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: Len 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.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/kernel/smpboot.c