From: Thomas Gleixner <[email protected]>
From: Thomas Gleixner <[email protected]>
The naming conventions in the delay code are confusing at best.
All delay variants use a loops argument and or variable which originates
from the original delay_loop() implementation. But all variants except
delay_loop() are based on TSC cycles.
Rename the argument to cycles and make it type u64 to avoid these weird
expansions to u64 in the functions.
Rename MWAITX_MAX_LOOPS to MWAITX_MAX_WAIT_CYCLES for the same reason
and fixup the comment of delay_mwaitx() as well.
Mark the delay_fn function pointer __ro_after_init and fixup the comment
for it.
No functional change and preparation for the upcoming TPAUSE based delay
variant.
[Kyung Min Park: Added __init to use_tsc_delay()]
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Kyung Min Park <[email protected]>
---
arch/x86/include/asm/delay.h | 2 +-
arch/x86/include/asm/mwait.h | 2 +-
arch/x86/lib/delay.c | 45 +++++++++++++++++++++++---------------------
3 files changed, 26 insertions(+), 23 deletions(-)
diff --git a/arch/x86/include/asm/delay.h b/arch/x86/include/asm/delay.h
index de9e784..bb91d7c 100644
--- a/arch/x86/include/asm/delay.h
+++ b/arch/x86/include/asm/delay.h
@@ -4,7 +4,7 @@
#include <asm-generic/delay.h>
-void use_tsc_delay(void);
+void __init use_tsc_delay(void);
void use_mwaitx_delay(void);
#endif /* _ASM_X86_DELAY_H */
diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index b809f11..a43b35b 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -20,7 +20,7 @@
#define MWAIT_ECX_INTERRUPT_BREAK 0x1
#define MWAITX_ECX_TIMER_ENABLE BIT(1)
-#define MWAITX_MAX_LOOPS ((u32)-1)
+#define MWAITX_MAX_WAIT_CYCLES UINT_MAX
#define MWAITX_DISABLE_CSTATES 0xf0
u32 get_umwait_control_msr(void);
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index c126571..887d52d 100644
--- a/arch/x86/lib/delay.c
+++ b/arch/x86/lib/delay.c
@@ -27,9 +27,19 @@
# include <asm/smp.h>
#endif
+static void delay_loop(u64 __loops);
+
+/*
+ * Calibration and selection of the delay mechanism happens only once
+ * during boot.
+ */
+static void (*delay_fn)(u64) __ro_after_init = delay_loop;
+
/* simple loop based delay: */
-static void delay_loop(unsigned long loops)
+static void delay_loop(u64 __loops)
{
+ unsigned long loops = (unsigned long)__loops;
+
asm volatile(
" test %0,%0 \n"
" jz 3f \n"
@@ -49,9 +59,9 @@ static void delay_loop(unsigned long loops)
}
/* TSC based delay: */
-static void delay_tsc(unsigned long __loops)
+static void delay_tsc(u64 cycles)
{
- u64 bclock, now, loops = __loops;
+ u64 bclock, now;
int cpu;
preempt_disable();
@@ -59,7 +69,7 @@ static void delay_tsc(unsigned long __loops)
bclock = rdtsc_ordered();
for (;;) {
now = rdtsc_ordered();
- if ((now - bclock) >= loops)
+ if ((now - bclock) >= cycles)
break;
/* Allow RT tasks to run */
@@ -77,7 +87,7 @@ static void delay_tsc(unsigned long __loops)
* counter for this CPU.
*/
if (unlikely(cpu != smp_processor_id())) {
- loops -= (now - bclock);
+ cycles -= (now - bclock);
cpu = smp_processor_id();
bclock = rdtsc_ordered();
}
@@ -87,24 +97,24 @@ static void delay_tsc(unsigned long __loops)
/*
* On some AMD platforms, MWAITX has a configurable 32-bit timer, that
- * counts with TSC frequency. The input value is the loop of the
- * counter, it will exit when the timer expires.
+ * counts with TSC frequency. The input value is the number of TSC cycles
+ * to wait. MWAITX will also exit when the timer expires.
*/
-static void delay_mwaitx(unsigned long __loops)
+static void delay_mwaitx(u64 cycles)
{
- u64 start, end, delay, loops = __loops;
+ u64 start, end, delay;
/*
* Timer value of 0 causes MWAITX to wait indefinitely, unless there
* is a store on the memory monitored by MONITORX.
*/
- if (loops == 0)
+ if (!cycles)
return;
start = rdtsc_ordered();
for (;;) {
- delay = min_t(u64, MWAITX_MAX_LOOPS, loops);
+ delay = min_t(u64, MWAITX_MAX_WAIT_CYCLES, cycles);
/*
* Use cpu_tss_rw as a cacheline-aligned, seldomly
@@ -121,22 +131,15 @@ static void delay_mwaitx(unsigned long __loops)
end = rdtsc_ordered();
- if (loops <= end - start)
+ if (cycles <= end - start)
break;
- loops -= end - start;
-
+ cycles -= end - start;
start = end;
}
}
-/*
- * Since we calibrate only once at boot, this
- * function should be set once at boot and not changed
- */
-static void (*delay_fn)(unsigned long) = delay_loop;
-
-void use_tsc_delay(void)
+void __init use_tsc_delay(void)
{
if (delay_fn == delay_loop)
delay_fn = delay_tsc;
--
2.7.4
Hi Kyung,
I love your patch! Yet something to improve:
[auto build test ERROR on tip/auto-latest]
[also build test ERROR on linus/master tip/x86/core linux/master v5.7-rc1 next-20200412]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
url: https://github.com/0day-ci/linux/commits/Kyung-Min-Park/x86-delay-Introduce-TPAUSE-instruction/20200411-073203
base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 1d625b673f4477a92277a2291be07fa82519ce15
config: i386-debian-10.3 (attached as .config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <[email protected]>
All errors (new ones prefixed by >>):
In file included from arch/x86/kernel/reboot_fixups_32.c:11:0:
>> arch/x86/include/asm/delay.h:7:13: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'use_tsc_delay'
void __init use_tsc_delay(void);
^~~~~~~~~~~~~
vim +7 arch/x86/include/asm/delay.h
6
> 7 void __init use_tsc_delay(void);
8 void use_mwaitx_delay(void);
9
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/[email protected]