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ia64: Update fsyscall gettime to use modern vsyscall_update

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John Stultz provided the outline for this patch back in May 2014 here:

	http://patches.linaro.org/patch/30501/

but I let this sit on the shelf for too long and in the intervening
years almost every field in "struct timekeeper" was changed. So this
is almost completely different from his original. Though the key change
in arch/ia64/kernel/fsys.S remains the same.

The core logic change with the updated vsyscall method is that we
preserve the base nanosecond value in shifted nanoseconds, which
allows us to avoid truncating and rounding up to the next nanosecond
every tick to avoid inconsistencies.

Thus the logic moved from
nsec = ((cycle_delta * mult)>>shift) + base_nsec;
to
nsec = ((cycle_delta * mult) + base_snsec) >> shift;

Cc: John Stultz <john.stultz@linaro.org>
Cc: linux-ia64@vger.kernel.org
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
Tony Luck 2017-10-31 10:43:39 -07:00
parent 0b07194bb5
commit d4d1fc61eb
5 changed files with 35 additions and 25 deletions
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2
arch/ia64/Kconfig
View file

@ -46,7 +46,7 @@ config IA64
select ARCH_TASK_STRUCT_ALLOCATOR
select ARCH_THREAD_STACK_ALLOCATOR
select ARCH_CLOCKSOURCE_DATA
select GENERIC_TIME_VSYSCALL_OLD
select GENERIC_TIME_VSYSCALL
select SYSCTL_ARCH_UNALIGN_NO_WARN
select HAVE_MOD_ARCH_SPECIFIC
select MODULES_USE_ELF_RELA

2
arch/ia64/kernel/asm-offsets.c
View file

@ -211,6 +211,8 @@ void foo(void)
BLANK();
DEFINE(IA64_TIMESPEC_TV_NSEC_OFFSET,
offsetof (struct timespec, tv_nsec));
DEFINE(IA64_TIME_SN_SPEC_SNSEC_OFFSET,
offsetof (struct time_sn_spec, snsec));
DEFINE(CLONE_SETTLS_BIT, 19);
#if CLONE_SETTLS != (1<<19)

8
arch/ia64/kernel/fsys.S
View file

@ -235,9 +235,9 @@ ENTRY(fsys_gettimeofday)
MOV_FROM_ITC(p8, p6, r2, r10) // CPU_TIMER. 36 clocks latency!!!
(p9) ld8 r2 = [r30] // MMIO_TIMER. Could also have latency issues..
(p13) ld8 r25 = [r19] // get itc_lastcycle value
ld8 r9 = [r22],IA64_TIMESPEC_TV_NSEC_OFFSET // tv_sec
ld8 r9 = [r22],IA64_TIME_SN_SPEC_SNSEC_OFFSET // sec
;;
ld8 r8 = [r22],-IA64_TIMESPEC_TV_NSEC_OFFSET // tv_nsec
ld8 r8 = [r22],-IA64_TIME_SN_SPEC_SNSEC_OFFSET // snsec
(p13) sub r3 = r25,r2 // Diff needed before comparison (thanks davidm)
;;
(p13) cmp.gt.unc p6,p7 = r3,r0 // check if it is less than last. p6,p7 cleared
@ -265,9 +265,9 @@ EX(.fail_efault, probe.w.fault r31, 3)
mf
;;
ld4 r10 = [r20] // gtod_lock.sequence
shr.u r2 = r2,r23 // shift by factor
;;
add r8 = r8,r2 // Add xtime.nsecs
;;
shr.u r8 = r8,r23 // shift by factor
cmp4.ne p7,p0 = r28,r10
(p7) br.cond.dpnt.few .time_redo // sequence number changed, redo
// End critical section.

10
arch/ia64/kernel/fsyscall_gtod_data.h
View file

@ -5,10 +5,16 @@
* fsyscall gettimeofday data
*/
/* like timespec, but includes "shifted nanoseconds" */
struct time_sn_spec {
u64 sec;
u64 snsec;
};
struct fsyscall_gtod_data_t {
seqcount_t seq;
struct timespec wall_time;
struct timespec monotonic_time;
struct time_sn_spec wall_time;
struct time_sn_spec monotonic_time;
u64 clk_mask;
u32 clk_mult;
u32 clk_shift;

38
arch/ia64/kernel/time.c
View file

@ -430,30 +430,32 @@ void update_vsyscall_tz(void)
{
}
void update_vsyscall_old(struct timespec *wall, struct timespec *wtm,
struct clocksource *c, u32 mult, u64 cycle_last)
void update_vsyscall(struct timekeeper *tk)
{
write_seqcount_begin(&fsyscall_gtod_data.seq);
/* copy fsyscall clock data */
fsyscall_gtod_data.clk_mask = c->mask;
fsyscall_gtod_data.clk_mult = mult;
fsyscall_gtod_data.clk_shift = c->shift;
fsyscall_gtod_data.clk_fsys_mmio = c->archdata.fsys_mmio;
fsyscall_gtod_data.clk_cycle_last = cycle_last;
/* copy vsyscall data */
fsyscall_gtod_data.clk_mask = tk->tkr_mono.mask;
fsyscall_gtod_data.clk_mult = tk->tkr_mono.mult;
fsyscall_gtod_data.clk_shift = tk->tkr_mono.shift;
fsyscall_gtod_data.clk_fsys_mmio = tk->tkr_mono.clock->archdata.fsys_mmio;
fsyscall_gtod_data.clk_cycle_last = tk->tkr_mono.cycle_last;
/* copy kernel time structures */
fsyscall_gtod_data.wall_time.tv_sec = wall->tv_sec;
fsyscall_gtod_data.wall_time.tv_nsec = wall->tv_nsec;
fsyscall_gtod_data.monotonic_time.tv_sec = wtm->tv_sec
+ wall->tv_sec;
fsyscall_gtod_data.monotonic_time.tv_nsec = wtm->tv_nsec
+ wall->tv_nsec;
fsyscall_gtod_data.wall_time.sec = tk->xtime_sec;
fsyscall_gtod_data.wall_time.snsec = tk->tkr_mono.xtime_nsec;
fsyscall_gtod_data.monotonic_time.sec = tk->xtime_sec
+ tk->wall_to_monotonic.tv_sec;
fsyscall_gtod_data.monotonic_time.snsec = tk->tkr_mono.xtime_nsec
+ ((u64)tk->wall_to_monotonic.tv_nsec
<< tk->tkr_mono.shift);
/* normalize */
while (fsyscall_gtod_data.monotonic_time.tv_nsec >= NSEC_PER_SEC) {
fsyscall_gtod_data.monotonic_time.tv_nsec -= NSEC_PER_SEC;
fsyscall_gtod_data.monotonic_time.tv_sec++;
while (fsyscall_gtod_data.monotonic_time.snsec >=
(((u64)NSEC_PER_SEC) << tk->tkr_mono.shift)) {
fsyscall_gtod_data.monotonic_time.snsec -=
((u64)NSEC_PER_SEC) << tk->tkr_mono.shift;
fsyscall_gtod_data.monotonic_time.sec++;
}
write_seqcount_end(&fsyscall_gtod_data.seq);