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>

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 51cc8c3..a67b971 100644 (file)
--- 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 c38d6a1..b20af76 100644 (file)
--- 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 ea33950..a6bcb31 100644 (file)
--- 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);