Re: [PATCH 2/5] arm64: perf: Implement correct cap_user_time
Hi Peter,
I love your patch! Yet something to improve:
[auto build test ERROR on tip/perf/core]
[also build test ERROR on arm64/for-next/core arm-perf/for-next/perf
linus/master v5.7-rc5 next-20200512]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
url:
https://github.com/0day-ci/linux/commits/Peter-Zijlstra/arm64-perf-Proper-cap_user_time-support/20200512-205141
base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
059c6d68cfc5f85ba3ab71d71a6de380016f7936
config: arm64-allyesconfig (attached as .config)
compiler: aarch64-linux-gcc (GCC) 9.3.0
reproduce:
wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O
~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day GCC_VERSION=9.3.0 make.cross
ARCH=arm64
If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot
All errors (new ones prefixed by >>):
arch/arm64/kernel/perf_event.c: In function 'arch_perf_update_userpage':
>> arch/arm64/kernel/perf_event.c:1205:12: error: 'struct perf_event_mmap_page'
>> has no member named 'shift'
1205 | if (userpg->shift == 32) {
|^~
arch/arm64/kernel/perf_event.c:1206:9: error: 'struct perf_event_mmap_page' has
no member named 'shift'
1206 | userpg->shift = 31;
| ^~
vim +1205 arch/arm64/kernel/perf_event.c
1165
1166 void arch_perf_update_userpage(struct perf_event *event,
1167 struct perf_event_mmap_page *userpg, u64
now)
1168 {
1169 struct clock_read_data *rd;
1170 unsigned int seq;
1171
1172 /*
1173 * Internal timekeeping for enabled/running/stopped times
1174 * is always computed with the sched_clock.
1175 */
1176 userpg->cap_user_time = 1;
1177 userpg->cap_user_time_zero = 1;
1178
1179 do {
1180 rd = sched_clock_read_begin();
1181
1182 userpg->time_mult = rd->mult;
1183 userpg->time_shift = rd->shift;
1184 userpg->time_zero = rd->epoch_ns;
1185
1186 /*
1187 * This isn't strictly correct, the ARM64 counter can be
1188 * 'short' and then we get funnies when it wraps. The
correct
1189 * thing would be to extend the perf ABI with a cycle
and mask
1190 * value, but because wrapping on ARM64 is very rare in
1191 * practise this 'works'.
1192 */
1193 userpg->time_zero -= (rd->epoch_cyc * rd->mult) >>
rd->shift;
1194
1195 } while (sched_clock_read_retry(seq));
1196
1197 userpg->time_offset = userpg->time_zero - now;
1198
1199 /*
1200 * time_shift is not expected to be greater than 31 due to
1201 * the original published conversion algorithm shifting a
1202 * 32-bit value (now specifies a 64-bit value) - refer
1203 * perf_event_mmap_page documentation in perf_event.h.
1204 */
> 1205 if (userpg->shift == 32) {
1206 userpg->shift = 31;
1207 userpg->time_mult >>= 1;
1208 }
1209
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-...@lists.01.org
.config.gz
Description: application/gzip
Re: [PATCH 2/5] arm64: perf: Implement correct cap_user_time
On Tue, May 12, 2020 at 10:03:01PM +0800, Leo Yan wrote:
> > + if (userpg->shift == 32) {
>
> Thanks a lot for the patch set, some typos:
>
> s/shift/time_shift
>
> > + userpg->shift = 31;
>
> s/shift/time_shift
Blergh.. so much for me not taking the time to dig out the arm64 cross
compiler :/ Sorry about that.
Re: [PATCH 2/5] arm64: perf: Implement correct cap_user_time
Hi Peter,
On Tue, May 12, 2020 at 02:41:00PM +0200, Peter Zijlstra wrote:
> As reported by Leo; the existing implementation is broken when the
> clock and counter don't intersect at 0.
>
> Use the sched_clock's struct clock_read_data information to correctly
> implement cap_user_time and cap_user_time_zero.
>
> Note that the ARM64 counter is architecturally only guaranteed to be
> 56bit wide (implementations are allowed to be wider) and the existing
> perf ABI cannot deal with wrap-around.
>
> This implementation should also be faster than the old; seeing how we
> don't need to recompute mult and shift all the time.
>
> Reported-by: Leo Yan
> Signed-off-by: Peter Zijlstra (Intel)
> ---
> arch/arm64/kernel/perf_event.c | 36 +++-
> 1 file changed, 27 insertions(+), 9 deletions(-)
>
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -19,6 +19,7 @@
> #include
> #include
> #include
> +#include
> #include
>
> /* ARMv8 Cortex-A53 specific event types. */
> @@ -1165,28 +1166,45 @@ device_initcall(armv8_pmu_driver_init)
> void arch_perf_update_userpage(struct perf_event *event,
> struct perf_event_mmap_page *userpg, u64 now)
> {
> - u32 freq;
> - u32 shift;
> + struct clock_read_data *rd;
> + unsigned int seq;
>
> /*
>* Internal timekeeping for enabled/running/stopped times
>* is always computed with the sched_clock.
>*/
> - freq = arch_timer_get_rate();
> userpg->cap_user_time = 1;
> + userpg->cap_user_time_zero = 1;
> +
> + do {
> + rd = sched_clock_read_begin();
> +
> + userpg->time_mult = rd->mult;
> + userpg->time_shift = rd->shift;
> + userpg->time_zero = rd->epoch_ns;
> +
> + /*
> + * This isn't strictly correct, the ARM64 counter can be
> + * 'short' and then we get funnies when it wraps. The correct
> + * thing would be to extend the perf ABI with a cycle and mask
> + * value, but because wrapping on ARM64 is very rare in
> + * practise this 'works'.
> + */
> + userpg->time_zero -= (rd->epoch_cyc * rd->mult) >> rd->shift;
> +
> + } while (sched_clock_read_retry(seq));
> +
> + userpg->time_offset = userpg->time_zero - now;
>
> - clocks_calc_mult_shift(>time_mult, , freq,
> - NSEC_PER_SEC, 0);
> /*
>* time_shift is not expected to be greater than 31 due to
>* the original published conversion algorithm shifting a
>* 32-bit value (now specifies a 64-bit value) - refer
>* perf_event_mmap_page documentation in perf_event.h.
>*/
> - if (shift == 32) {
> - shift = 31;
> + if (userpg->shift == 32) {
Thanks a lot for the patch set, some typos:
s/shift/time_shift
> + userpg->shift = 31;
s/shift/time_shift
Thanks,
Leo
> userpg->time_mult >>= 1;
> }
> - userpg->time_shift = (u16)shift;
> - userpg->time_offset = -now;
> +
> }
>
>
[PATCH 2/5] arm64: perf: Implement correct cap_user_time
As reported by Leo; the existing implementation is broken when the
clock and counter don't intersect at 0.
Use the sched_clock's struct clock_read_data information to correctly
implement cap_user_time and cap_user_time_zero.
Note that the ARM64 counter is architecturally only guaranteed to be
56bit wide (implementations are allowed to be wider) and the existing
perf ABI cannot deal with wrap-around.
This implementation should also be faster than the old; seeing how we
don't need to recompute mult and shift all the time.
Reported-by: Leo Yan
Signed-off-by: Peter Zijlstra (Intel)
---
arch/arm64/kernel/perf_event.c | 36 +++-
1 file changed, 27 insertions(+), 9 deletions(-)
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -19,6 +19,7 @@
#include
#include
#include
+#include
#include
/* ARMv8 Cortex-A53 specific event types. */
@@ -1165,28 +1166,45 @@ device_initcall(armv8_pmu_driver_init)
void arch_perf_update_userpage(struct perf_event *event,
struct perf_event_mmap_page *userpg, u64 now)
{
- u32 freq;
- u32 shift;
+ struct clock_read_data *rd;
+ unsigned int seq;
/*
* Internal timekeeping for enabled/running/stopped times
* is always computed with the sched_clock.
*/
- freq = arch_timer_get_rate();
userpg->cap_user_time = 1;
+ userpg->cap_user_time_zero = 1;
+
+ do {
+ rd = sched_clock_read_begin();
+
+ userpg->time_mult = rd->mult;
+ userpg->time_shift = rd->shift;
+ userpg->time_zero = rd->epoch_ns;
+
+ /*
+* This isn't strictly correct, the ARM64 counter can be
+* 'short' and then we get funnies when it wraps. The correct
+* thing would be to extend the perf ABI with a cycle and mask
+* value, but because wrapping on ARM64 is very rare in
+* practise this 'works'.
+*/
+ userpg->time_zero -= (rd->epoch_cyc * rd->mult) >> rd->shift;
+
+ } while (sched_clock_read_retry(seq));
+
+ userpg->time_offset = userpg->time_zero - now;
- clocks_calc_mult_shift(>time_mult, , freq,
- NSEC_PER_SEC, 0);
/*
* time_shift is not expected to be greater than 31 due to
* the original published conversion algorithm shifting a
* 32-bit value (now specifies a 64-bit value) - refer
* perf_event_mmap_page documentation in perf_event.h.
*/
- if (shift == 32) {
- shift = 31;
+ if (userpg->shift == 32) {
+ userpg->shift = 31;
userpg->time_mult >>= 1;
}
- userpg->time_shift = (u16)shift;
- userpg->time_offset = -now;
+
}
