arch/ia64/kernel/sys_ia64.c | 26 ++++++++++++++++++++++++++ arch/ia64/kernel/syscalls/syscall.tbl | 2 +- 2 files changed, 27 insertions(+), 1 deletion(-)
clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses
ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few
times slower than 1ns. Usually 2-3ns.
clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and
reported 0.04s precision (1/HZ value).
In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly
when it noticed precision discrepancy.
Before the change:
clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision.
After the change:
clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision.
The patch is based on matoro's fix. It adds a bit of explanation why we
need to special-case arch-specific clock_getres().
CC: linux-ia64@vger.kernel.org
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sergei Trofimovich <slyich@gmail.com>
---
arch/ia64/kernel/sys_ia64.c | 26 ++++++++++++++++++++++++++
arch/ia64/kernel/syscalls/syscall.tbl | 2 +-
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/arch/ia64/kernel/sys_ia64.c b/arch/ia64/kernel/sys_ia64.c
index e14db25146c2..d5d47eb4608e 100644
--- a/arch/ia64/kernel/sys_ia64.c
+++ b/arch/ia64/kernel/sys_ia64.c
@@ -166,3 +166,29 @@ ia64_mremap (unsigned long addr, unsigned long old_len, unsigned long new_len, u
force_successful_syscall_return();
return addr;
}
+
+asmlinkage long
+ia64_clock_getres(const clockid_t which_clock, struct __kernel_timespec __user *tp)
+{
+ /*
+ * ia64's clock_gettime() syscall is implemented as a vdso call
+ * fsys_clock_gettime(). Currently it handles only
+ * CLOCK_REALTIME and CLOCK_MONOTONIC. Both are based on
+ * 'ar.itc' counter which gets incremented at a constant
+ * frequency. It's usually 400MHz, ~2.5x times slower than CPU
+ * clock frequency. Which is almost a 1ns hrtimer, but not quite.
+ *
+ * Let's special-case these timers to report correct precision
+ * based on ITC frequency and not HZ frequency for supported
+ * clocks.
+ */
+ switch (which_clock) {
+ case CLOCK_REALTIME:
+ case CLOCK_MONOTONIC:
+ s64 tick_ns = DIV_ROUND_UP(NSEC_PER_SEC, local_cpu_data->itc_freq);
+ struct timespec64 rtn_tp = ns_to_timespec64(tick_ns);
+ return put_timespec64(&rtn_tp, tp);
+ }
+
+ return sys_clock_getres(which_clock, tp);
+}
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 78b1d03e86e1..72c929d9902b 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -240,7 +240,7 @@
228 common timer_delete sys_timer_delete
229 common clock_settime sys_clock_settime
230 common clock_gettime sys_clock_gettime
-231 common clock_getres sys_clock_getres
+231 common clock_getres ia64_clock_getres
232 common clock_nanosleep sys_clock_nanosleep
233 common fstatfs64 sys_fstatfs64
234 common statfs64 sys_statfs64
--
2.37.1On Mon, 15 Aug 2022 06:49:44 +0100 Sergei Trofimovich <slyich@gmail.com> wrote: > clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses > ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few > times slower than 1ns. Usually 2-3ns. > > clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and > reported 0.04s precision (1/HZ value). > > In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly > when it noticed precision discrepancy. > > Before the change: > > clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision. > > After the change: > > clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision. > > The patch is based on matoro's fix. It adds a bit of explanation why we > need to special-case arch-specific clock_getres(). > It would be best (and nice) to include the original developer's Signed-off-by: and to Cc Émeric Maschino if possible? Could you please take care of these paperwork issues?
On Wed, 17 Aug 2022 12:21:03 -0700 Andrew Morton <akpm@linux-foundation.org> wrote: > On Mon, 15 Aug 2022 06:49:44 +0100 Sergei Trofimovich <slyich@gmail.com> wrote: > > > clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses > > ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few > > times slower than 1ns. Usually 2-3ns. > > > > clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and > > reported 0.04s precision (1/HZ value). > > > > In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly > > when it noticed precision discrepancy. > > > > Before the change: > > > > clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision. > > > > After the change: > > > > clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision. > > > > The patch is based on matoro's fix. It adds a bit of explanation why we > > need to special-case arch-specific clock_getres(). > > > > It would be best (and nice) to include the original developer's > Signed-off-by: and to Cc Émeric Maschino if possible? > > Could you please take care of these paperwork issues? Sounds good! I'll use matoro's nickname as is for S-o-B the way matoro is comfortable with to share it. Will add Émeric in v2 and send out in a few minutes. -- Sergei
clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses
ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few
times slower than 1ns. Usually 2-3ns.
clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and
reported 0.04s precision (1/HZ value).
In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly
when it noticed precision discrepancy.
Before the change:
clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision.
After the change:
clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision.
The patch is based on matoro's fix. I added a bit of explanation why we
need to special-case arch-specific clock_getres().
CC: Émeric Maschino <emeric.maschino@gmail.com>
CC: linux-ia64@vger.kernel.org
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: matoro <matoro_mailinglist_kernel@matoro.tk>
Signed-off-by: Sergei Trofimovich <slyich@gmail.com>
---
Change since v1:
- No code or in-code comment change
- CCed Émeric
- Added matoro's S-O-B the way matoro comfortable with
- Fixed Subject typo s/clock_getre/clock_getres/
arch/ia64/kernel/sys_ia64.c | 26 ++++++++++++++++++++++++++
arch/ia64/kernel/syscalls/syscall.tbl | 2 +-
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/arch/ia64/kernel/sys_ia64.c b/arch/ia64/kernel/sys_ia64.c
index e14db25146c2..d5d47eb4608e 100644
--- a/arch/ia64/kernel/sys_ia64.c
+++ b/arch/ia64/kernel/sys_ia64.c
@@ -166,3 +166,29 @@ ia64_mremap (unsigned long addr, unsigned long old_len, unsigned long new_len, u
force_successful_syscall_return();
return addr;
}
+
+asmlinkage long
+ia64_clock_getres(const clockid_t which_clock, struct __kernel_timespec __user *tp)
+{
+ /*
+ * ia64's clock_gettime() syscall is implemented as a vdso call
+ * fsys_clock_gettime(). Currently it handles only
+ * CLOCK_REALTIME and CLOCK_MONOTONIC. Both are based on
+ * 'ar.itc' counter which gets incremented at a constant
+ * frequency. It's usually 400MHz, ~2.5x times slower than CPU
+ * clock frequency. Which is almost a 1ns hrtimer, but not quite.
+ *
+ * Let's special-case these timers to report correct precision
+ * based on ITC frequency and not HZ frequency for supported
+ * clocks.
+ */
+ switch (which_clock) {
+ case CLOCK_REALTIME:
+ case CLOCK_MONOTONIC:
+ s64 tick_ns = DIV_ROUND_UP(NSEC_PER_SEC, local_cpu_data->itc_freq);
+ struct timespec64 rtn_tp = ns_to_timespec64(tick_ns);
+ return put_timespec64(&rtn_tp, tp);
+ }
+
+ return sys_clock_getres(which_clock, tp);
+}
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 78b1d03e86e1..72c929d9902b 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -240,7 +240,7 @@
228 common timer_delete sys_timer_delete
229 common clock_settime sys_clock_settime
230 common clock_gettime sys_clock_gettime
-231 common clock_getres sys_clock_getres
+231 common clock_getres ia64_clock_getres
232 common clock_nanosleep sys_clock_nanosleep
233 common fstatfs64 sys_fstatfs64
234 common statfs64 sys_statfs64
--
2.37.1
Hi Andrew, I came up with the prototype for this patch, but it was based entirely on Sergei's investigation which was documented in https://bugs.gentoo.org/596382. I asked him to send it upstream because I'm unable to attach my realname to it due to my job. I can place a signed-off-by with my handle but I understand that's normally against kernel policy which is why I didn't. Either way the bulk of the work belongs to Sergei, I just scribbled it down, and he cleaned it up for this submission. -------- Original Message -------- Subject: Re: [PATCH] ia64: fix clock_getre(CLOCK_MONOTONIC) to report ITC frequency Date: 2022-08-17 15:21 From: Andrew Morton <akpm@linux-foundation.org> To: Sergei Trofimovich <slyich@gmail.com> On Mon, 15 Aug 2022 06:49:44 +0100 Sergei Trofimovich <slyich@gmail.com> wrote: > clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses > ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few > times slower than 1ns. Usually 2-3ns. > > clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and > reported 0.04s precision (1/HZ value). > > In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly > when it noticed precision discrepancy. > > Before the change: > > clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision. > > After the change: > > clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision. > > The patch is based on matoro's fix. It adds a bit of explanation why we > need to special-case arch-specific clock_getres(). > It would be best (and nice) to include the original developer's Signed-off-by: and to Cc Émeric Maschino if possible? Could you please take care of these paperwork issues?
On Wed, 17 Aug 2022 17:57:42 -0400 matoro <matoro_mailinglist_kernel@matoro.tk> wrote: > Hi Andrew, I came up with the prototype for this patch, but it was based > entirely on Sergei's investigation which was documented in > https://bugs.gentoo.org/596382. I asked him to send it upstream because > I'm unable to attach my realname to it due to my job. In that case it's unclear that your Signed-off-by: is appropriate? : Developer's Certificate of Origin 1.1 : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ : : By making a contribution to this project, I certify that: : : (a) The contribution was created in whole or in part by me and I : have the right to submit it under the open source license : indicated in the file; or : : (b) The contribution is based upon previous work that, to the best : of my knowledge, is covered under an appropriate open source : license and I have the right under that license to submit that : work with modifications, whether created in whole or in part : by me, under the same open source license (unless I am : permitted to submit under a different license), as indicated : in the file; or : : (c) The contribution was provided directly to me by some other : person who certified (a), (b) or (c) and I have not modified : it. : : (d) I understand and agree that this project and the contribution : are public and that a record of the contribution (including all : personal information I submit with it, including my sign-off) is : maintained indefinitely and may be redistributed consistent with : this project or the open source license(s) involved. > I can place a > signed-off-by with my handle but I understand that's normally against > kernel policy which is why I didn't. Either way the bulk of the work > belongs to Sergei, I just scribbled it down, and he cleaned it up for > this submission. I think I'll switch it to a Cc: :)
clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses
ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few
times slower than 1ns. Usually 2-3ns.
clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and
reported 0.04s precision (1/HZ value).
In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly
when it noticed precision discrepancy.
Before the change:
clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision.
After the change:
clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision.
The patch is based on matoro's fix. I added a bit of explanation why we
need to special-case arch-specific clock_getres().
CC: Émeric Maschino <emeric.maschino@gmail.com>
CC: linux-ia64@vger.kernel.org
CC: Andrew Morton <akpm@linux-foundation.org>
CC: matoro <matoro_mailinglist_kernel@matoro.tk>
Signed-off-by: Sergei Trofimovich <slyich@gmail.com>
---
Change since v2:
- Moved matoro to CC
Change since v1:
- No code or in-code comment change
- CCed Émeric
- Added matoro's S-O-B the way matoro comfortable with
- Fixed Subject typo s/clock_getre/clock_getres/
arch/ia64/kernel/sys_ia64.c | 26 ++++++++++++++++++++++++++
arch/ia64/kernel/syscalls/syscall.tbl | 2 +-
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/arch/ia64/kernel/sys_ia64.c b/arch/ia64/kernel/sys_ia64.c
index e14db25146c2..d5d47eb4608e 100644
--- a/arch/ia64/kernel/sys_ia64.c
+++ b/arch/ia64/kernel/sys_ia64.c
@@ -166,3 +166,29 @@ ia64_mremap (unsigned long addr, unsigned long old_len, unsigned long new_len, u
force_successful_syscall_return();
return addr;
}
+
+asmlinkage long
+ia64_clock_getres(const clockid_t which_clock, struct __kernel_timespec __user *tp)
+{
+ /*
+ * ia64's clock_gettime() syscall is implemented as a vdso call
+ * fsys_clock_gettime(). Currently it handles only
+ * CLOCK_REALTIME and CLOCK_MONOTONIC. Both are based on
+ * 'ar.itc' counter which gets incremented at a constant
+ * frequency. It's usually 400MHz, ~2.5x times slower than CPU
+ * clock frequency. Which is almost a 1ns hrtimer, but not quite.
+ *
+ * Let's special-case these timers to report correct precision
+ * based on ITC frequency and not HZ frequency for supported
+ * clocks.
+ */
+ switch (which_clock) {
+ case CLOCK_REALTIME:
+ case CLOCK_MONOTONIC:
+ s64 tick_ns = DIV_ROUND_UP(NSEC_PER_SEC, local_cpu_data->itc_freq);
+ struct timespec64 rtn_tp = ns_to_timespec64(tick_ns);
+ return put_timespec64(&rtn_tp, tp);
+ }
+
+ return sys_clock_getres(which_clock, tp);
+}
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 78b1d03e86e1..72c929d9902b 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -240,7 +240,7 @@
228 common timer_delete sys_timer_delete
229 common clock_settime sys_clock_settime
230 common clock_gettime sys_clock_gettime
-231 common clock_getres sys_clock_getres
+231 common clock_getres ia64_clock_getres
232 common clock_nanosleep sys_clock_nanosleep
233 common fstatfs64 sys_fstatfs64
234 common statfs64 sys_statfs64
--
2.37.2
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