* [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
@ 2019-10-21 12:52 ` Huacai Chen
0 siblings, 0 replies; 10+ messages in thread
From: Huacai Chen @ 2019-10-21 12:52 UTC (permalink / raw)
To: Andy Lutomirski
Cc: Thomas Gleixner, Vincenzo Frascino, chenhuacai, linux-kernel,
Huacai Chen, stable, Arnd Bergmann, Paul Burton, linux-mips,
linux-arm-kernel
In do_hres(), we currently use whether the return value of __arch_get_
hw_counter() is negative to indicate fallback, but this is not a good
idea because:
1, ARM64 returns ULL_MAX but MIPS returns 0 when clock_mode is invalid;
2, For a 64bit counter, a "negative" value of counter is actually valid.
It is sure that MIPS has a bug when clock_mode is invalid and should
return ULL_MAX as ARM64 does (Vincenzo has already submitted a patch).
But do_hres() can still be improved so we use U64_MAX as the only
"invalid" return value -- this is still not fully correct, but it is
the simplest fix and has no problem in most cases (we can hardly see a
64bit counter overflow).
By the way, currently update_vdso_data() and update_vsyscall_tz() rely
on __arch_use_vsyscall(), which causes __cvdso_clock_getres() and some
other functions get wrong results when clock_mode is invalid. So, we
update vdso data unconditionally.
Fixes: 00b26474c2f1613d7ab894c5 ("lib/vdso: Provide generic VDSO implementation")
Fixes: 44f57d788e7deecb50484353 ("timekeeping: Provide a generic update_vsyscall() implementation")
Cc: stable@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Huacai Chen <chenhc@lemote.com>
---
kernel/time/vsyscall.c | 9 +++------
lib/vdso/gettimeofday.c | 2 +-
2 files changed, 4 insertions(+), 7 deletions(-)
diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index 4bc37ac..5ee0f77 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -110,8 +110,7 @@ void update_vsyscall(struct timekeeper *tk)
nsec = nsec + tk->wall_to_monotonic.tv_nsec;
vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec);
- if (__arch_use_vsyscall(vdata))
- update_vdso_data(vdata, tk);
+ update_vdso_data(vdata, tk);
__arch_update_vsyscall(vdata, tk);
@@ -124,10 +123,8 @@ void update_vsyscall_tz(void)
{
struct vdso_data *vdata = __arch_get_k_vdso_data();
- if (__arch_use_vsyscall(vdata)) {
- vdata[CS_HRES_COARSE].tz_minuteswest = sys_tz.tz_minuteswest;
- vdata[CS_HRES_COARSE].tz_dsttime = sys_tz.tz_dsttime;
- }
+ vdata[CS_HRES_COARSE].tz_minuteswest = sys_tz.tz_minuteswest;
+ vdata[CS_HRES_COARSE].tz_dsttime = sys_tz.tz_dsttime;
__arch_sync_vdso_data(vdata);
}
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index e630e7f..5a31643 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
cycles = __arch_get_hw_counter(vd->clock_mode);
ns = vdso_ts->nsec;
last = vd->cycle_last;
- if (unlikely((s64)cycles < 0))
+ if (unlikely(cycles == U64_MAX))
return -1;
ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
--
2.7.0
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
@ 2019-10-21 12:52 ` Huacai Chen
0 siblings, 0 replies; 10+ messages in thread
From: Huacai Chen @ 2019-10-21 12:52 UTC (permalink / raw)
To: Andy Lutomirski
Cc: Arnd Bergmann, chenhuacai, linux-kernel, stable, linux-mips,
Paul Burton, Huacai Chen, Thomas Gleixner, Vincenzo Frascino,
linux-arm-kernel
In do_hres(), we currently use whether the return value of __arch_get_
hw_counter() is negative to indicate fallback, but this is not a good
idea because:
1, ARM64 returns ULL_MAX but MIPS returns 0 when clock_mode is invalid;
2, For a 64bit counter, a "negative" value of counter is actually valid.
It is sure that MIPS has a bug when clock_mode is invalid and should
return ULL_MAX as ARM64 does (Vincenzo has already submitted a patch).
But do_hres() can still be improved so we use U64_MAX as the only
"invalid" return value -- this is still not fully correct, but it is
the simplest fix and has no problem in most cases (we can hardly see a
64bit counter overflow).
By the way, currently update_vdso_data() and update_vsyscall_tz() rely
on __arch_use_vsyscall(), which causes __cvdso_clock_getres() and some
other functions get wrong results when clock_mode is invalid. So, we
update vdso data unconditionally.
Fixes: 00b26474c2f1613d7ab894c5 ("lib/vdso: Provide generic VDSO implementation")
Fixes: 44f57d788e7deecb50484353 ("timekeeping: Provide a generic update_vsyscall() implementation")
Cc: stable@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Huacai Chen <chenhc@lemote.com>
---
kernel/time/vsyscall.c | 9 +++------
lib/vdso/gettimeofday.c | 2 +-
2 files changed, 4 insertions(+), 7 deletions(-)
diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index 4bc37ac..5ee0f77 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -110,8 +110,7 @@ void update_vsyscall(struct timekeeper *tk)
nsec = nsec + tk->wall_to_monotonic.tv_nsec;
vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec);
- if (__arch_use_vsyscall(vdata))
- update_vdso_data(vdata, tk);
+ update_vdso_data(vdata, tk);
__arch_update_vsyscall(vdata, tk);
@@ -124,10 +123,8 @@ void update_vsyscall_tz(void)
{
struct vdso_data *vdata = __arch_get_k_vdso_data();
- if (__arch_use_vsyscall(vdata)) {
- vdata[CS_HRES_COARSE].tz_minuteswest = sys_tz.tz_minuteswest;
- vdata[CS_HRES_COARSE].tz_dsttime = sys_tz.tz_dsttime;
- }
+ vdata[CS_HRES_COARSE].tz_minuteswest = sys_tz.tz_minuteswest;
+ vdata[CS_HRES_COARSE].tz_dsttime = sys_tz.tz_dsttime;
__arch_sync_vdso_data(vdata);
}
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index e630e7f..5a31643 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
cycles = __arch_get_hw_counter(vd->clock_mode);
ns = vdso_ts->nsec;
last = vd->cycle_last;
- if (unlikely((s64)cycles < 0))
+ if (unlikely(cycles == U64_MAX))
return -1;
ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult);
--
2.7.0
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
2019-10-21 12:52 ` Huacai Chen
@ 2019-10-21 14:52 ` Thomas Gleixner
-1 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2019-10-21 14:52 UTC (permalink / raw)
To: Huacai Chen
Cc: Andy Lutomirski, Vincenzo Frascino, chenhuacai, linux-kernel,
stable, Arnd Bergmann, Paul Burton, linux-mips, linux-arm-kernel
On Mon, 21 Oct 2019, Huacai Chen wrote:
> @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> cycles = __arch_get_hw_counter(vd->clock_mode);
> ns = vdso_ts->nsec;
> last = vd->cycle_last;
> - if (unlikely((s64)cycles < 0))
> + if (unlikely(cycles == U64_MAX))
> return -1;
That used to create worse code than the weird (s64) type cast which has the
same effect. Did you double check that there is no change?
Thanks,
tglx
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
@ 2019-10-21 14:52 ` Thomas Gleixner
0 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2019-10-21 14:52 UTC (permalink / raw)
To: Huacai Chen
Cc: Arnd Bergmann, chenhuacai, linux-kernel, stable, linux-mips,
Paul Burton, Andy Lutomirski, Vincenzo Frascino,
linux-arm-kernel
On Mon, 21 Oct 2019, Huacai Chen wrote:
> @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> cycles = __arch_get_hw_counter(vd->clock_mode);
> ns = vdso_ts->nsec;
> last = vd->cycle_last;
> - if (unlikely((s64)cycles < 0))
> + if (unlikely(cycles == U64_MAX))
> return -1;
That used to create worse code than the weird (s64) type cast which has the
same effect. Did you double check that there is no change?
Thanks,
tglx
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
2019-10-21 14:52 ` Thomas Gleixner
@ 2019-10-21 14:58 ` Thomas Gleixner
-1 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2019-10-21 14:58 UTC (permalink / raw)
To: Huacai Chen
Cc: Andy Lutomirski, Vincenzo Frascino, chenhuacai, linux-kernel,
stable, Arnd Bergmann, Paul Burton, linux-mips, linux-arm-kernel
On Mon, 21 Oct 2019, Thomas Gleixner wrote:
> On Mon, 21 Oct 2019, Huacai Chen wrote:
> > @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> > cycles = __arch_get_hw_counter(vd->clock_mode);
> > ns = vdso_ts->nsec;
> > last = vd->cycle_last;
> > - if (unlikely((s64)cycles < 0))
> > + if (unlikely(cycles == U64_MAX))
> > return -1;
>
> That used to create worse code than the weird (s64) type cast which has the
> same effect. Did you double check that there is no change?
It still does for 32bit.
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
@ 2019-10-21 14:58 ` Thomas Gleixner
0 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2019-10-21 14:58 UTC (permalink / raw)
To: Huacai Chen
Cc: Arnd Bergmann, chenhuacai, linux-kernel, stable, linux-mips,
Paul Burton, Andy Lutomirski, Vincenzo Frascino,
linux-arm-kernel
On Mon, 21 Oct 2019, Thomas Gleixner wrote:
> On Mon, 21 Oct 2019, Huacai Chen wrote:
> > @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> > cycles = __arch_get_hw_counter(vd->clock_mode);
> > ns = vdso_ts->nsec;
> > last = vd->cycle_last;
> > - if (unlikely((s64)cycles < 0))
> > + if (unlikely(cycles == U64_MAX))
> > return -1;
>
> That used to create worse code than the weird (s64) type cast which has the
> same effect. Did you double check that there is no change?
It still does for 32bit.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
2019-10-21 14:58 ` Thomas Gleixner
@ 2019-10-22 2:42 ` Huacai Chen
-1 siblings, 0 replies; 10+ messages in thread
From: Huacai Chen @ 2019-10-22 2:42 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Andy Lutomirski, Vincenzo Frascino, LKML, stable, Arnd Bergmann,
Paul Burton, open list:MIPS, linux-arm-kernel
Hi, Thomas,
If we use (s64)cycles < 0, then how to solve the problem that a 64bit
counter become negative?
Maybe we can change the "invalid" value from U64_MAX to 0? I think
the performance of "cycles == 0" is better than "cycles == U64_MAX".
Huacai
On Mon, Oct 21, 2019 at 10:58 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Mon, 21 Oct 2019, Thomas Gleixner wrote:
>
> > On Mon, 21 Oct 2019, Huacai Chen wrote:
> > > @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> > > cycles = __arch_get_hw_counter(vd->clock_mode);
> > > ns = vdso_ts->nsec;
> > > last = vd->cycle_last;
> > > - if (unlikely((s64)cycles < 0))
> > > + if (unlikely(cycles == U64_MAX))
> > > return -1;
> >
> > That used to create worse code than the weird (s64) type cast which has the
> > same effect. Did you double check that there is no change?
>
> It still does for 32bit.
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
@ 2019-10-22 2:42 ` Huacai Chen
0 siblings, 0 replies; 10+ messages in thread
From: Huacai Chen @ 2019-10-22 2:42 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Arnd Bergmann, LKML, stable, open list:MIPS, Paul Burton,
Andy Lutomirski, Vincenzo Frascino, linux-arm-kernel
Hi, Thomas,
If we use (s64)cycles < 0, then how to solve the problem that a 64bit
counter become negative?
Maybe we can change the "invalid" value from U64_MAX to 0? I think
the performance of "cycles == 0" is better than "cycles == U64_MAX".
Huacai
On Mon, Oct 21, 2019 at 10:58 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Mon, 21 Oct 2019, Thomas Gleixner wrote:
>
> > On Mon, 21 Oct 2019, Huacai Chen wrote:
> > > @@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk,
> > > cycles = __arch_get_hw_counter(vd->clock_mode);
> > > ns = vdso_ts->nsec;
> > > last = vd->cycle_last;
> > > - if (unlikely((s64)cycles < 0))
> > > + if (unlikely(cycles == U64_MAX))
> > > return -1;
> >
> > That used to create worse code than the weird (s64) type cast which has the
> > same effect. Did you double check that there is no change?
>
> It still does for 32bit.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
2019-10-22 2:42 ` Huacai Chen
@ 2019-10-23 8:48 ` Thomas Gleixner
-1 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2019-10-23 8:48 UTC (permalink / raw)
To: Huacai Chen
Cc: Andy Lutomirski, Vincenzo Frascino, LKML, stable, Arnd Bergmann,
Paul Burton, open list:MIPS, linux-arm-kernel
On Tue, 22 Oct 2019, Huacai Chen wrote:
https://people.kernel.org/tglx/notes-about-netiquette
Look for Toppost
> If we use (s64)cycles < 0, then how to solve the problem that a 64bit
> counter become negative?
I doubt that you will be able to observe that. A 64bit value becomes
negative after 1<<63 cycles, i.e. at 1GHz thats 292 years of uptime.
What's your problem?
Thanks,
tglx
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally
@ 2019-10-23 8:48 ` Thomas Gleixner
0 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2019-10-23 8:48 UTC (permalink / raw)
To: Huacai Chen
Cc: Arnd Bergmann, LKML, stable, open list:MIPS, Paul Burton,
Andy Lutomirski, Vincenzo Frascino, linux-arm-kernel
On Tue, 22 Oct 2019, Huacai Chen wrote:
https://people.kernel.org/tglx/notes-about-netiquette
Look for Toppost
> If we use (s64)cycles < 0, then how to solve the problem that a 64bit
> counter become negative?
I doubt that you will be able to observe that. A 64bit value becomes
negative after 1<<63 cycles, i.e. at 1GHz thats 292 years of uptime.
What's your problem?
Thanks,
tglx
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2019-10-23 8:48 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-21 12:52 [PATCH 110/110] lib/vdso: Improve do_hres() and update vdso data unconditionally Huacai Chen
2019-10-21 12:52 ` Huacai Chen
2019-10-21 14:52 ` Thomas Gleixner
2019-10-21 14:52 ` Thomas Gleixner
2019-10-21 14:58 ` Thomas Gleixner
2019-10-21 14:58 ` Thomas Gleixner
2019-10-22 2:42 ` Huacai Chen
2019-10-22 2:42 ` Huacai Chen
2019-10-23 8:48 ` Thomas Gleixner
2019-10-23 8:48 ` Thomas Gleixner
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