diff options
| author | Len Brown | 2015-08-16 11:45:46 -0400 |
|---|---|---|
| committer | Ingo Molnar | 2015-08-17 10:42:27 +0200 |
| commit | 2d99af8e8fd6c2dea11ab539f7aba69c37b845b4 (patch) | |
| tree | 17243b7a328ca1f3c4170ed64d4e045b62a128ef /arch/x86/kernel | |
| parent | 6e38f1e79d16f4fa9e5cf06792500e11c96a6f84 (diff) | |
x86/smpboot: Remove udelay(100) when polling cpu_callin_map
After the BSP sends INIT/SIPI/SIP to the AP and sees the AP
in the cpu_initialized_map, it sets the AP loose via the
cpu_callout_map, and waits for it via the cpu_callin_map.
The BSP polls the cpu_callin_map with a udelay(100)
and a schedule() in each iteration.
The udelay(100) adds no value.
For example, on my 4-CPU dekstop, the AP finishes
cpu_callin() in under 70 usec and sets the cpu_callin_mask.
The BSP, however, doesn't see that setting until over 30 usec
later, because it was still running its udelay(100)
when the AP finished.
Deleting the udelay(100) in the cpu_callin_mask polling loop,
saves from 0 to 100 usec per Application Processor.
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/0aade12eabeb89a688c929fe80856eaea0544bb7.1439739165.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel')
| -rw-r--r-- | arch/x86/kernel/smpboot.c | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 9ad88fb0a303..310b6f0bf6f7 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -926,7 +926,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) * for the MTRR work(triggered by the AP coming online) * to be completed in the stop machine context. */ - udelay(100); schedule(); } } |