alpha: Allow HZ to be configured

With the 1024Hz default, we spend 50% of QEMU emulation
processing timer interrupts.

Signed-off-by: Richard Henderson <rth@twiddle.net>

3 files changed, 59 insertions, 11 deletions

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 51cc8c353164..a67b971c830a 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -627,9 +627,41 @@ config VERBOSE_MCHECK_ON
 
           Take the default (1) unless you want more control or more info.
 
+choice
+        prompt "Timer interrupt frequency (HZ)?"
+        default HZ_128 if ALPHA_QEMU
+        default HZ_1200 if ALPHA_RAWHIDE
+        default HZ_1024
+        ---help---
+          The frequency at which timer interrupts occur.  A high frequency
+          minimizes latency, whereas a low frequency minimizes overhead of
+          process accounting.  The later effect is especially significant
+          when being run under QEMU.
+
+          Note that some Alpha hardware cannot change the interrupt frequency
+          of the timer.  If unsure, say 1024 (or 1200 for Rawhide).
+
+        config HZ_32
+                bool "32 Hz"
+        config HZ_64
+                bool "64 Hz"
+        config HZ_128
+                bool "128 Hz"
+        config HZ_256
+                bool "256 Hz"
+        config HZ_1024
+                bool "1024 Hz"
+        config HZ_1200
+                bool "1200 Hz"
+endchoice
+
 config HZ
-        int
-        default 1200 if ALPHA_RAWHIDE
+        int 
+        default 32 if HZ_32
+        default 64 if HZ_64
+        default 128 if HZ_128
+        default 256 if HZ_256
+        default 1200 if HZ_1200
         default 1024
 
 source "drivers/pci/Kconfig"
diff --git a/arch/alpha/kernel/setup.c b/arch/alpha/kernel/setup.c
index c38d6a1b9066..b20af76f12c1 100644
--- a/arch/alpha/kernel/setup.c
+++ b/arch/alpha/kernel/setup.c
@@ -1218,6 +1218,7 @@ show_cpuinfo(struct seq_file *f, void *slot)
         char *systype_name;
         char *sysvariation_name;
         int nr_processors;
+        unsigned long timer_freq;
 
         cpu_index = (unsigned) (cpu->type - 1);
         cpu_name = "Unknown";
@@ -1229,6 +1230,12 @@ show_cpuinfo(struct seq_file *f, void *slot)
 
         nr_processors = get_nr_processors(cpu, hwrpb->nr_processors);
 
+#if CONFIG_HZ == 1024 || CONFIG_HZ == 1200
+        timer_freq = (100UL * hwrpb->intr_freq) / 4096;
+#else
+        timer_freq = 100UL * CONFIG_HZ;
+#endif
+
         seq_printf(f, "cpu\t\t\t: Alpha\n"
                       "cpu model\t\t: %s\n"
                       "cpu variation\t\t: %ld\n"
@@ -1254,8 +1261,7 @@ show_cpuinfo(struct seq_file *f, void *slot)
                        (char*)hwrpb->ssn,
                        est_cycle_freq ? : hwrpb->cycle_freq,
                        est_cycle_freq ? "est." : "",
-                       hwrpb->intr_freq / 4096,
-                       (100 * hwrpb->intr_freq / 4096) % 100,
+                       timer_freq / 100, timer_freq % 100,
                        hwrpb->pagesize,
                        hwrpb->pa_bits,
                        hwrpb->max_asn,
diff --git a/arch/alpha/kernel/time.c b/arch/alpha/kernel/time.c
index ea3395036556..a6bcb3113d81 100644
--- a/arch/alpha/kernel/time.c
+++ b/arch/alpha/kernel/time.c
@@ -201,16 +201,26 @@ irqreturn_t timer_interrupt(int irq, void *dev)
 void __init
 common_init_rtc(void)
 {
-        unsigned char x;
+        unsigned char x, sel = 0;
 
         /* Reset periodic interrupt frequency.  */
-        x = CMOS_READ(RTC_FREQ_SELECT) & 0x3f;
-        /* Test includes known working values on various platforms
-           where 0x26 is wrong; we refuse to change those. */
-        if (x != 0x26 && x != 0x25 && x != 0x19 && x != 0x06) {
-                printk("Setting RTC_FREQ to 1024 Hz (%x)\n", x);
-                CMOS_WRITE(0x26, RTC_FREQ_SELECT);
+#if CONFIG_HZ == 1024 || CONFIG_HZ == 1200
+        x = CMOS_READ(RTC_FREQ_SELECT) & 0x3f;
+        /* Test includes known working values on various platforms
+           where 0x26 is wrong; we refuse to change those. */
+        if (x != 0x26 && x != 0x25 && x != 0x19 && x != 0x06) {
+                sel = RTC_REF_CLCK_32KHZ + 6;
         }
+#elif CONFIG_HZ == 256 || CONFIG_HZ == 128 || CONFIG_HZ == 64 || CONFIG_HZ == 32
+        sel = RTC_REF_CLCK_32KHZ + __builtin_ffs(32768 / CONFIG_HZ);
+#else
+# error "Unknown HZ from arch/alpha/Kconfig"
+#endif
+        if (sel) {
+                printk(KERN_INFO "Setting RTC_FREQ to %d Hz (%x)\n",
+                       CONFIG_HZ, sel);
+                CMOS_WRITE(sel, RTC_FREQ_SELECT);
+        }
 
         /* Turn on periodic interrupts.  */
         x = CMOS_READ(RTC_CONTROL);