Commit a9bcaa02 authored by Len Brown's avatar Len Brown Committed by Ingo Molnar

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: 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>
parent 2d99af8e
......@@ -665,7 +665,8 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
/*
* Give the other CPU some time to accept the IPI.
*/
udelay(300);
if (init_udelay)
udelay(300);
pr_debug("Startup point 1\n");
......@@ -675,7 +676,8 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
/*
* Give the other CPU some time to accept the IPI.
*/
udelay(200);
if (init_udelay)
udelay(200);
if (maxlvt > 3) /* Due to the Pentium erratum 3AP. */
apic_write(APIC_ESR, 0);
......
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