Commit c8118c6c authored by Eric Dumazet's avatar Eric Dumazet Committed by Andi Kleen
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[PATCH] x86-64: vsyscall_gtod_data diet and vgettimeofday() fix 



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: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 272a3713

arch/x86_64/kernel/vsyscall.c

+36 −17
Original line number Diff line number Diff line
@@ -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;



	/* open coded 'struct timespec' */

	time_t		wall_time_sec;

	u32		wall_time_nsec;



	int		sysctl_enabled;

	struct timeval wall_time_tv;

	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;

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