init: skip calibration delay if previously done
Sameer Nanda [Tue, 26 Jul 2011 00:13:29 +0000 (17:13 -0700)]
For each CPU, do the calibration delay only once.  For subsequent calls,
use the cached per-CPU value of loops_per_jiffy.

This saves about 200ms of resume time on dual core Intel Atom N5xx based
systems.  This helps bring down the kernel resume time on such systems
from about 500ms to about 300ms.

[akpm@linux-foundation.org: make cpu_loops_per_jiffy static]
[akpm@linux-foundation.org: clean up message text]
[akpm@linux-foundation.org: fix things up after upstream rmk changes]
Signed-off-by: Sameer Nanda <snanda@chromium.org>
Cc: Phil Carmody <ext-phil.2.carmody@nokia.com>
Cc: Andrew Worsley <amworsley@gmail.com>
Cc: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/calibrate.c

index aae2f40..24df797 100644 (file)
@@ -9,6 +9,7 @@
 #include <linux/init.h>
 #include <linux/timex.h>
 #include <linux/smp.h>
+#include <linux/percpu.h>
 
 unsigned long lpj_fine;
 unsigned long preset_lpj;
@@ -243,12 +244,19 @@ recalibrate:
        return lpj;
 }
 
+static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
+
 void __cpuinit calibrate_delay(void)
 {
        unsigned long lpj;
        static bool printed;
+       int this_cpu = smp_processor_id();
 
-       if (preset_lpj) {
+       if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
+               lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
+               pr_info("Calibrating delay loop (skipped) "
+                               "already calibrated this CPU");
+       } else if (preset_lpj) {
                lpj = preset_lpj;
                if (!printed)
                        pr_info("Calibrating delay loop (skipped) "
@@ -266,6 +274,7 @@ void __cpuinit calibrate_delay(void)
                        pr_info("Calibrating delay loop... ");
                lpj = calibrate_delay_converge();
        }
+       per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
        if (!printed)
                pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
                        lpj/(500000/HZ),