| Message ID | 20190401115152.32751-2-vincenzo.frascino@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fix vDSO clock_getres() | expand |
On Mon, Apr 01, 2019 at 12:51:48PM +0100, Vincenzo Frascino wrote: > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > index 2d419006ad43..47ba72345739 100644 > --- a/arch/arm64/kernel/vdso.c > +++ b/arch/arm64/kernel/vdso.c > @@ -245,6 +245,8 @@ void update_vsyscall(struct timekeeper *tk) > vdso_data->cs_shift = tk->tkr_mono.shift; > } > > + vdso_data->hrtimer_res = hrtimer_resolution; > + > smp_wmb(); > ++vdso_data->tb_seq_count; > } > diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S > index c39872a7b03c..7a2cd2f8e13a 100644 > --- a/arch/arm64/kernel/vdso/gettimeofday.S > +++ b/arch/arm64/kernel/vdso/gettimeofday.S > @@ -296,32 +296,35 @@ ENDPROC(__kernel_clock_gettime) > /* int __kernel_clock_getres(clockid_t clock_id, struct timespec *res); */ > ENTRY(__kernel_clock_getres) > .cfi_startproc > + adr vdso_data, _vdso_data > cmp w0, #CLOCK_REALTIME > ccmp w0, #CLOCK_MONOTONIC, #0x4, ne > ccmp w0, #CLOCK_MONOTONIC_RAW, #0x4, ne > - b.ne 1f > + b.ne 2f > > - ldr x2, 5f > - b 2f > -1: > +1: /* Get hrtimer_res */ > + seqcnt_acquire > + syscall_check fail=5f > + ldr x2, [vdso_data, #CLOCK_REALTIME_RES] > + seqcnt_check fail=1b > + b 3f > +2: We talked briefly but I'm still confused why we need the fallback to the syscall here if archdata.vdso_direct is false. Is it because if the timer driver code sets vdso_direct to false, we don't don't support highres timers? If my understanding is correct, you may want to move the hrtimer_res setting in update_vsyscall() to the !use_syscall block.
Hi Catalin, On 15/04/2019 18:35, Catalin Marinas wrote: > On Mon, Apr 01, 2019 at 12:51:48PM +0100, Vincenzo Frascino wrote: >> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c >> index 2d419006ad43..47ba72345739 100644 >> --- a/arch/arm64/kernel/vdso.c >> +++ b/arch/arm64/kernel/vdso.c >> @@ -245,6 +245,8 @@ void update_vsyscall(struct timekeeper *tk) >> vdso_data->cs_shift = tk->tkr_mono.shift; >> } >> >> + vdso_data->hrtimer_res = hrtimer_resolution; >> + >> smp_wmb(); >> ++vdso_data->tb_seq_count; >> } >> diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S >> index c39872a7b03c..7a2cd2f8e13a 100644 >> --- a/arch/arm64/kernel/vdso/gettimeofday.S >> +++ b/arch/arm64/kernel/vdso/gettimeofday.S >> @@ -296,32 +296,35 @@ ENDPROC(__kernel_clock_gettime) >> /* int __kernel_clock_getres(clockid_t clock_id, struct timespec *res); */ >> ENTRY(__kernel_clock_getres) >> .cfi_startproc >> + adr vdso_data, _vdso_data >> cmp w0, #CLOCK_REALTIME >> ccmp w0, #CLOCK_MONOTONIC, #0x4, ne >> ccmp w0, #CLOCK_MONOTONIC_RAW, #0x4, ne >> - b.ne 1f >> + b.ne 2f >> >> - ldr x2, 5f >> - b 2f >> -1: >> +1: /* Get hrtimer_res */ >> + seqcnt_acquire >> + syscall_check fail=5f >> + ldr x2, [vdso_data, #CLOCK_REALTIME_RES] >> + seqcnt_check fail=1b >> + b 3f >> +2: > > We talked briefly but I'm still confused why we need the fallback to the > syscall here if archdata.vdso_direct is false. Is it because if the > timer driver code sets vdso_direct to false, we don't don't support > highres timers? If my understanding is correct, you may want to move the > hrtimer_res setting in update_vsyscall() to the !use_syscall block. > Ok, so let me try to provide more details on what I mentioned yesterday: - clock_getres syscall follows the rules of what defined in posix-timers.c - based on the clock_id that, for this purpose, can be separated in coarse and non-coarse calls either posix_get_coarse_res() or posix_get_hrtimer_res(). - if clock id is set to a coarse clock and posix_get_coarse_res() is invoked, happens what follows: static int posix_get_coarse_res(const clockid_t which_clock, struct timespec64 *tp) { *tp = ktime_to_timespec64(KTIME_LOW_RES); return 0; } Note that since CONFIG_1HZ seems not supported (jiffies.h) by the kernel in this case we do not need rounding in our vDSO implementation. - if clock id is set to non-coarse and posix_get_hrtimer_res() is invoked, happens the following: static int posix_get_hrtimer_res(clockid_t which_clock, struct timespec64 *tp) { tp->tv_sec = 0; tp->tv_nsec = hrtimer_resolution; return 0; } hrtimer_resolution can be high res or low res depending on the call of hrtimer_switch_to_hres(). For us the only way to preserve the correct value is to keep it in the vdso data page. - The assembly code mimics exactly the same behaviour detailed above, with one difference: the one related to the use_syscall parameter which is specific to arm64. The use_syscall parameter is set by arm_arch_timer and consumed by update_vsyscall(). To mirror what update_vsyscall does in update_vsyscall() I check "syscall_check fail=5f" in clock_getres vdso function. Said that, even if functionally it is the same thing, I think it is logically more correct to have hrtimer_res setting inside the !use_syscall block, hence I am going to change it in the next iteration. Please let me know your thoughts.
On Tue, Apr 16, 2019 at 01:42:58PM +0100, Vincenzo Frascino wrote: > On 15/04/2019 18:35, Catalin Marinas wrote: > > On Mon, Apr 01, 2019 at 12:51:48PM +0100, Vincenzo Frascino wrote: > >> +1: /* Get hrtimer_res */ > >> + seqcnt_acquire > >> + syscall_check fail=5f > >> + ldr x2, [vdso_data, #CLOCK_REALTIME_RES] > >> + seqcnt_check fail=1b > >> + b 3f > >> +2: > > > > We talked briefly but I'm still confused why we need the fallback to the > > syscall here if archdata.vdso_direct is false. Is it because if the > > timer driver code sets vdso_direct to false, we don't don't support > > highres timers? If my understanding is correct, you may want to move the > > hrtimer_res setting in update_vsyscall() to the !use_syscall block. > > > > Ok, so let me try to provide more details on what I mentioned yesterday: > - clock_getres syscall follows the rules of what defined in posix-timers.c > - based on the clock_id that, for this purpose, can be separated in coarse and > non-coarse calls either posix_get_coarse_res() or posix_get_hrtimer_res(). > - if clock id is set to a coarse clock and posix_get_coarse_res() is invoked, > happens what follows: > > static int posix_get_coarse_res(const clockid_t which_clock, > struct timespec64 *tp) > { > *tp = ktime_to_timespec64(KTIME_LOW_RES); > return 0; > } > > Note that since CONFIG_1HZ seems not supported (jiffies.h) by the kernel in this > case we do not need rounding in our vDSO implementation. > > - if clock id is set to non-coarse and posix_get_hrtimer_res() is invoked, > happens the following: > > static int posix_get_hrtimer_res(clockid_t which_clock, struct timespec64 *tp) > { > tp->tv_sec = 0; > tp->tv_nsec = hrtimer_resolution; > return 0; > } > > hrtimer_resolution can be high res or low res depending on the call of > hrtimer_switch_to_hres(). For us the only way to preserve the correct value is > to keep it in the vdso data page. > > - The assembly code mimics exactly the same behaviour detailed above, with one > difference: the one related to the use_syscall parameter which is specific to arm64. > The use_syscall parameter is set by arm_arch_timer and consumed by > update_vsyscall(). To mirror what update_vsyscall does in update_vsyscall() I > check "syscall_check fail=5f" in clock_getres vdso function. > > Said that, even if functionally it is the same thing, I think it is logically > more correct to have hrtimer_res setting inside the !use_syscall block, hence I > am going to change it in the next iteration. > > Please let me know your thoughts. I think you can ignore the syscall_check, just like we seem to do for CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE in clock_gettime(). Will
diff --git a/arch/arm64/include/asm/vdso_datapage.h b/arch/arm64/include/asm/vdso_datapage.h index 2b9a63771eda..f89263c8e11a 100644 --- a/arch/arm64/include/asm/vdso_datapage.h +++ b/arch/arm64/include/asm/vdso_datapage.h @@ -38,6 +38,7 @@ struct vdso_data { __u32 tz_minuteswest; /* Whacky timezone stuff */ __u32 tz_dsttime; __u32 use_syscall; + __u32 hrtimer_res; }; #endif /* !__ASSEMBLY__ */ diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index 7f40dcbdd51d..e10e2a5d9ddc 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -94,7 +94,7 @@ int main(void) DEFINE(CLOCK_REALTIME, CLOCK_REALTIME); DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC); DEFINE(CLOCK_MONOTONIC_RAW, CLOCK_MONOTONIC_RAW); - DEFINE(CLOCK_REALTIME_RES, MONOTONIC_RES_NSEC); + DEFINE(CLOCK_REALTIME_RES, offsetof(struct vdso_data, hrtimer_res)); DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE); DEFINE(CLOCK_MONOTONIC_COARSE,CLOCK_MONOTONIC_COARSE); DEFINE(CLOCK_COARSE_RES, LOW_RES_NSEC); diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c index 2d419006ad43..47ba72345739 100644 --- a/arch/arm64/kernel/vdso.c +++ b/arch/arm64/kernel/vdso.c @@ -245,6 +245,8 @@ void update_vsyscall(struct timekeeper *tk) vdso_data->cs_shift = tk->tkr_mono.shift; } + vdso_data->hrtimer_res = hrtimer_resolution; + smp_wmb(); ++vdso_data->tb_seq_count; } diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S index c39872a7b03c..7a2cd2f8e13a 100644 --- a/arch/arm64/kernel/vdso/gettimeofday.S +++ b/arch/arm64/kernel/vdso/gettimeofday.S @@ -296,32 +296,35 @@ ENDPROC(__kernel_clock_gettime) /* int __kernel_clock_getres(clockid_t clock_id, struct timespec *res); */ ENTRY(__kernel_clock_getres) .cfi_startproc + adr vdso_data, _vdso_data cmp w0, #CLOCK_REALTIME ccmp w0, #CLOCK_MONOTONIC, #0x4, ne ccmp w0, #CLOCK_MONOTONIC_RAW, #0x4, ne - b.ne 1f + b.ne 2f - ldr x2, 5f - b 2f -1: +1: /* Get hrtimer_res */ + seqcnt_acquire + syscall_check fail=5f + ldr x2, [vdso_data, #CLOCK_REALTIME_RES] + seqcnt_check fail=1b + b 3f +2: cmp w0, #CLOCK_REALTIME_COARSE ccmp w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne - b.ne 4f + b.ne 5f ldr x2, 6f -2: - cbz x1, 3f +3: + cbz x1, 4f stp xzr, x2, [x1] -3: /* res == NULL. */ +4: /* res == NULL. */ mov w0, wzr ret -4: /* Syscall fallback. */ +5: /* Syscall fallback. */ mov x8, #__NR_clock_getres svc #0 ret -5: - .quad CLOCK_REALTIME_RES 6: .quad CLOCK_COARSE_RES .cfi_endproc
clock_getres in the vDSO library has to preserve the same behaviour of posix_get_hrtimer_res(). In particular, posix_get_hrtimer_res() does: sec = 0; ns = hrtimer_resolution; and hrtimer_resolution depends on the enablement of the high resolution timers that can happen either at compile or at run time. Fix the arm64 vdso implementation of clock_getres keeping a copy of hrtimer_resolution in vdso data and using that directly. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> --- arch/arm64/include/asm/vdso_datapage.h | 1 + arch/arm64/kernel/asm-offsets.c | 2 +- arch/arm64/kernel/vdso.c | 2 ++ arch/arm64/kernel/vdso/gettimeofday.S | 25 ++++++++++++++----------- 4 files changed, 18 insertions(+), 12 deletions(-)