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Subject[RFC PATCH 04/10] alpha: Allow HZ to be configured
Date
With the 1024Hz default, we spend 50% of QEMU emulation
processing timer interrupts.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
arch/alpha/Kconfig | 36 ++++++++++++++++++++++++++++++++++--
arch/alpha/kernel/setup.c | 10 ++++++++--
arch/alpha/kernel/time.c | 24 +++++++++++++++++-------
3 files changed, 59 insertions(+), 11 deletions(-)

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 2053f215..5991a99 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -628,9 +628,41 @@ 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
--- 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 e336694..7938bf9 100644
--- a/arch/alpha/kernel/time.c
+++ b/arch/alpha/kernel/time.c
@@ -203,16 +203,26 @@ 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);
--
1.8.1.4


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