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.comSigned-off-by: Ingo Molnar <mingo@kernel.org>
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