From a9bcaa02a5104ace6a9d9e4a9cd9192a9e7744d6 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Sun, 16 Aug 2015 11:45:47 -0400 Subject: [PATCH] x86/smpboot: Remove SIPI delays from cpu_up() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Andy Lutomirski Cc: Arjan van de Ven Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Dave Hansen Cc: Igor Mammedov Cc: Jan H. Schönherr Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Zhu Guihua Link: http://lkml.kernel.org/r/a5dfdbc8fbfdd813784da204aad5677fe459ac37.1439739165.git.len.brown@intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smpboot.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 310b6f0bf6f7..674026455fee 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -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); -- 2.30.2