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[PATCH] x86-64: vsyscall_gtod_data diet and vgettimeofday() fix

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Current vsyscall_gtod_data is large (3 or 4 cache lines dirtied at timer
interrupt). We can shrink it to exactly 64 bytes (1 cache line on AMD64)

Instead of copying a whole struct clocksource, we copy only needed fields.

I deleted an unused field : offset_base

This patch fixes one oddity in vgettimeofday(): It can returns a timeval with
tv_usec = 1000000. Maybe not a bug, but why not doing the right thing ?

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
Eric Dumazet 2007-05-02 19:27:11 +02:00 committed by Andi Kleen
parent 272a3713bb
commit c8118c6c07
1 changed files with 36 additions and 17 deletions
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53
arch/x86_64/kernel/vsyscall.c
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@ -51,13 +51,28 @@
asm("" : "=r" (v) : "0" (x)); \
((v - VSYSCALL_FIRST_PAGE) + __pa_symbol(&__vsyscall_0)); })
/*
* vsyscall_gtod_data contains data that is :
* - readonly from vsyscalls
* - writen by timer interrupt or systcl (/proc/sys/kernel/vsyscall64)
* Try to keep this structure as small as possible to avoid cache line ping pongs
*/
struct vsyscall_gtod_data_t {
seqlock_t lock;
int sysctl_enabled;
struct timeval wall_time_tv;
seqlock_t lock;
/* open coded 'struct timespec' */
time_t wall_time_sec;
u32 wall_time_nsec;
int sysctl_enabled;
struct timezone sys_tz;
cycle_t offset_base;
struct clocksource clock;
struct { /* extract of a clocksource struct */
cycle_t (*vread)(void);
cycle_t cycle_last;
cycle_t mask;
u32 mult;
u32 shift;
} clock;
};
int __vgetcpu_mode __section_vgetcpu_mode;
@ -73,9 +88,13 @@ void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
/* copy vsyscall data */
vsyscall_gtod_data.clock = *clock;
vsyscall_gtod_data.wall_time_tv.tv_sec = wall_time->tv_sec;
vsyscall_gtod_data.wall_time_tv.tv_usec = wall_time->tv_nsec/1000;
vsyscall_gtod_data.clock.vread = clock->vread;
vsyscall_gtod_data.clock.cycle_last = clock->cycle_last;
vsyscall_gtod_data.clock.mask = clock->mask;
vsyscall_gtod_data.clock.mult = clock->mult;
vsyscall_gtod_data.clock.shift = clock->shift;
vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
vsyscall_gtod_data.sys_tz = sys_tz;
write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
}
@ -110,7 +129,8 @@ static __always_inline long time_syscall(long *t)
static __always_inline void do_vgettimeofday(struct timeval * tv)
{
cycle_t now, base, mask, cycle_delta;
unsigned long seq, mult, shift, nsec_delta;
unsigned seq;
unsigned long mult, shift, nsec;
cycle_t (*vread)(void);
do {
seq = read_seqbegin(&__vsyscall_gtod_data.lock);
@ -126,21 +146,20 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)
mult = __vsyscall_gtod_data.clock.mult;
shift = __vsyscall_gtod_data.clock.shift;
*tv = __vsyscall_gtod_data.wall_time_tv;
tv->tv_sec = __vsyscall_gtod_data.wall_time_sec;
nsec = __vsyscall_gtod_data.wall_time_nsec;
} while (read_seqretry(&__vsyscall_gtod_data.lock, seq));
/* calculate interval: */
cycle_delta = (now - base) & mask;
/* convert to nsecs: */
nsec_delta = (cycle_delta * mult) >> shift;
nsec += (cycle_delta * mult) >> shift;
/* convert to usecs and add to timespec: */
tv->tv_usec += nsec_delta / NSEC_PER_USEC;
while (tv->tv_usec > USEC_PER_SEC) {
while (nsec >= NSEC_PER_SEC) {
tv->tv_sec += 1;
tv->tv_usec -= USEC_PER_SEC;
nsec -= NSEC_PER_SEC;
}
tv->tv_usec = nsec / NSEC_PER_USEC;
}
int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
@ -159,7 +178,7 @@ time_t __vsyscall(1) vtime(time_t *t)
time_t result;
if (unlikely(!__vsyscall_gtod_data.sysctl_enabled))
return time_syscall(t);
result = __vsyscall_gtod_data.wall_time_tv.tv_sec;
result = __vsyscall_gtod_data.wall_time_sec;
if (t)
*t = result;
return result;