Re: Linus rollup

Andrew Morton
2003-01-30T01:10:50Z

"David S. Miller" <davem@redhat.com> wrote:
>
> From: Andrew Morton <akpm@digeo.com>
> Date: Wed, 29 Jan 2003 15:12:06 -0800
>
> But that would be a separate patch. _all_ we are doing here is fixing and
> optimising the xtime_lock problems. We should seek to do that with
> "equivalent transformations".
>
> I agree, do this and arch people can tweak later.

Stephen has already tweaked. Hopefully Andi and David can review this
sometime:

This is an optimisation to the ia64, ia32 and x86_64 do_gettimeofday() code
above and beyond the base frlock work.

Patch from Stephen Hemminger <shemminger@osdl.org>

* Don't need to disable interrupts on ia64, x86_64 or ia32 with TSC
getttimeofday. Disabling interrupts is noticeably slower ~3% so
would really like to only do it if necessary.

* Some more cleanup of frlock.h in the macro's that aren't being used yet.

arch/i386/kernel/time.c | 7 +++----
arch/i386/kernel/timers/timer_pit.c | 7 +++----
arch/ia64/kernel/time.c | 5 ++---
include/linux/frlock.h | 8 ++++++--
i386/kernel/apm.c | 0
5 files changed, 14 insertions(+), 13 deletions(-)

diff -puN arch/i386/kernel/apm.c~do_gettimeofday-speedup arch/i386/kernel/apm.c
diff -puN arch/i386/kernel/time.c~do_gettimeofday-speedup arch/i386/kernel/time.c
--- 25/arch/i386/kernel/time.c~do_gettimeofday-speedup Wed Jan 29 16:39:41 2003
+++ 25-akpm/arch/i386/kernel/time.c Wed Jan 29 16:39:41 2003
@@ -86,22 +86,21 @@ struct timer_opts* timer = &timer_none;
*/
void do_gettimeofday(struct timeval *tv)
{
- unsigned long flags;
unsigned long seq;
unsigned long usec, sec;

do {
- seq = fr_read_begin_irqsave(&xtime_lock, flags);
+ seq = fr_read_begin(&xtime_lock);

usec = timer->get_offset();
{
unsigned long lost = jiffies - wall_jiffies;
- if (lost)
+ if (unlikely(lost != 0))
usec += lost * (1000000 / HZ);
}
sec = xtime.tv_sec;
usec += (xtime.tv_nsec / 1000);
- } while (unlikely(seq != fr_read_end_irqrestore(&xtime_lock, flags)));
+ } while (unlikely(seq != fr_read_end(&xtime_lock)));

while (usec >= 1000000) {
usec -= 1000000;
diff -puN arch/i386/kernel/timers/timer_pit.c~do_gettimeofday-speedup arch/i386/kernel/timers/timer_pit.c
--- 25/arch/i386/kernel/timers/timer_pit.c~do_gettimeofday-speedup Wed Jan 29 16:39:41 2003
+++ 25-akpm/arch/i386/kernel/timers/timer_pit.c Wed Jan 29 16:39:41 2003
@@ -76,7 +76,7 @@ static void delay_pit(unsigned long loop
static unsigned long get_offset_pit(void)
{
int count;
-
+ unsigned long flags;
static int count_p = LATCH; /* for the first call after boot */
static unsigned long jiffies_p = 0;

@@ -85,8 +85,7 @@ static unsigned long get_offset_pit(void
*/
unsigned long jiffies_t;

- /* gets recalled with irq locally disabled */
- spin_lock(&i8253_lock);
+ spin_lock_irqsave(&i8253_lock, flags);
/* timer count may underflow right here */
outb_p(0x00, 0x43); /* latch the count ASAP */

@@ -108,7 +107,7 @@ static unsigned long get_offset_pit(void
count = LATCH - 1;
}

- spin_unlock(&i8253_lock);
+ spin_unlock_irqrestore(&i8253_lock, flags);

/*
* avoiding timer inconsistencies (they are rare, but they happen)...
diff -puN arch/ia64/kernel/time.c~do_gettimeofday-speedup arch/ia64/kernel/time.c
--- 25/arch/ia64/kernel/time.c~do_gettimeofday-speedup Wed Jan 29 16:39:41 2003
+++ 25-akpm/arch/ia64/kernel/time.c Wed Jan 29 16:39:41 2003
@@ -117,11 +117,10 @@ do_settimeofday (struct timeval *tv)
void
do_gettimeofday (struct timeval *tv)
{
- unsigned long flags;
unsigned long seq, usec, sec, old;

do {
- seq = fr_read_begin_irqsave(&xtime_lock, flags);
+ seq = fr_read_begin(&xtime_lock);
usec = gettimeoffset();

/*
@@ -138,7 +137,7 @@ do_gettimeofday (struct timeval *tv)

sec = xtime.tv_sec;
usec += xtime.tv_nsec / 1000;
- } while (seq != fr_read_end_irqrestore(&xtime_lock, flags));
+ } while (seq != fr_read_end(&xtime_lock));

while (usec >= 1000000) {
diff -puN include/linux/frlock.h~do_gettimeofday-speedup include/linux/frlock.h
--- 25/include/linux/frlock.h~do_gettimeofday-speedup Wed Jan 29 16:39:41 2003
+++ 25-akpm/include/linux/frlock.h Wed Jan 29 16:42:15 2003
@@ -64,6 +64,9 @@ static inline void fr_write_end(frlock_t
preempt_enable();
}

+/* Lock out other writers and update the count.
+ * Acts like a normal spin_lock/unlock.
+ */
static inline void fr_write_lock(frlock_t *rw)
{
spin_lock(&rw->lock);
@@ -82,11 +85,12 @@ static inline int fr_write_trylock(frloc

if (ret) {
++rw->pre_sequence;
- wmb();
+ mb();
}
return ret;
}

+/* Start of read calculation -- fetch last complete writer token */
static inline unsigned fr_read_begin(const frlock_t *rw)
{
unsigned ret = rw->post_sequence;
@@ -95,6 +99,7 @@ static inline unsigned fr_read_begin(con

}

+/* End of reader calculation -- fetch last writer start token */
static inline unsigned fr_read_end(const frlock_t *rw)
{
rmb();
@@ -128,4 +133,3 @@ static inline unsigned fr_read_end(const
})

#endif /* __LINUX_FRLOCK_H */
-

_