Since the switch to generic entry, an interrupt from user mode
accounts user time twice: once in arch_interrupt_enter_prepare()
and again in arch_enter_from_user_mode(), which irqentry_enter()
invokes for the same interrupt:
arch_interrupt_enter_prepare()
account_cpu_user_entry() /* first */
irqentry_enter()
arch_enter_from_user_mode()
account_cpu_user_entry() /* second */
The second call charges the same interval again, because
account_cpu_user_entry() accumulates the time spent in user mode
since the last return to user space.
The two calls come from the GENERIC_ENTRY preparation series,
where each step was a no-op on its own. Commit 09a9d3a8499d
("powerpc: introduce arch_enter_from_user_mode") added the hook
with the user-time accounting in it, but nothing called it yet.
Commit 893082ac769b ("powerpc: Prepare for IRQ entry exit")
copied interrupt_enter_prepare() verbatim into entry-common.h as
arch_interrupt_enter_prepare(); that copy was equally unused, as
handlers still called interrupt_enter_prepare().
Commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
made both live. On the syscall side it did the full conversion:
system_call_exception() now accounts once through the hook via
syscall_enter_from_user_mode(), rather than calling
account_cpu_user_entry() directly. On the interrupt side it
switched the handler macros to arch_interrupt_enter_prepare()
followed by irqentry_enter(), which also runs the hook, but the
accounting in arch_interrupt_enter_prepare() was not removed to
match. The double accounting starts with that commit.
With CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y this roughly doubles the
reported user time of any workload that takes interrupts. The
other accounting modes compile account_cpu_user_entry() to an
empty stub, so they are not affected.
Remove the accounting from arch_interrupt_enter_prepare() and rely
on arch_enter_from_user_mode(), which already runs for both
syscalls and interrupts. The duplicate account_stolen_time() call
is removed the same way.
On a pseries LPAR a busy loop reports 6s user time in 3s elapsed
(~210% CPU) before the fix, and 3s (~105% CPU) after it:
$ python3 -c 'while True: pass' &
$ sleep 3; ps -p $! -o etime,time,pcpu
ELAPSED TIME %CPU
Before 00:03 00:00:06 210
After 00:03 00:00:03 105
A 50% load reports ~70% usr / 30% idle before the fix, and
~49% usr / 51% idle after it:
$ taskset -c 6 stress-ng --cpu 1 --cpu-load 50 &
$ mpstat -P 6 1
CPU %usr %idle
Before 6 69.74 30.26
After 6 48.51 50.50
Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
Signed-off-by: Aboorva Devarajan <redacted>
---
Changes in v2:
- Explain which commits introduced each accounting call and how
they overlapped in commit message.
- Drop the code comment.
v1: https://lore.kernel.org/linuxppc-dev/20260902050628.2553909-1-aboorvad@linux.ibm.com/
arch/powerpc/include/asm/entry-common.h | 2 --
1 file changed, 2 deletions(-)
Le 04/09/2026 à 04:58, Aboorva Devarajan a écrit :
Since the switch to generic entry, an interrupt from user mode
accounts user time twice: once in arch_interrupt_enter_prepare()
and again in arch_enter_from_user_mode(), which irqentry_enter()
invokes for the same interrupt:
arch_interrupt_enter_prepare()
account_cpu_user_entry() /* first */
irqentry_enter()
arch_enter_from_user_mode()
account_cpu_user_entry() /* second */
The second call charges the same interval again, because
account_cpu_user_entry() accumulates the time spent in user mode
since the last return to user space.
The two calls come from the GENERIC_ENTRY preparation series,
where each step was a no-op on its own. Commit 09a9d3a8499d
("powerpc: introduce arch_enter_from_user_mode") added the hook
with the user-time accounting in it, but nothing called it yet.
Commit 893082ac769b ("powerpc: Prepare for IRQ entry exit")
copied interrupt_enter_prepare() verbatim into entry-common.h as
arch_interrupt_enter_prepare(); that copy was equally unused, as
handlers still called interrupt_enter_prepare().
Commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
made both live. On the syscall side it did the full conversion:
system_call_exception() now accounts once through the hook via
syscall_enter_from_user_mode(), rather than calling
account_cpu_user_entry() directly. On the interrupt side it
switched the handler macros to arch_interrupt_enter_prepare()
followed by irqentry_enter(), which also runs the hook, but the
accounting in arch_interrupt_enter_prepare() was not removed to
match. The double accounting starts with that commit.
With CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y this roughly doubles the
reported user time of any workload that takes interrupts. The
other accounting modes compile account_cpu_user_entry() to an
empty stub, so they are not affected.
Remove the accounting from arch_interrupt_enter_prepare() and rely
on arch_enter_from_user_mode(), which already runs for both
syscalls and interrupts. The duplicate account_stolen_time() call
is removed the same way.
On a pseries LPAR a busy loop reports 6s user time in 3s elapsed
(~210% CPU) before the fix, and 3s (~105% CPU) after it:
$ python3 -c 'while True: pass' &
$ sleep 3; ps -p $! -o etime,time,pcpu
ELAPSED TIME %CPU
Before 00:03 00:00:06 210
After 00:03 00:00:03 105
A 50% load reports ~70% usr / 30% idle before the fix, and
~49% usr / 51% idle after it:
$ taskset -c 6 stress-ng --cpu 1 --cpu-load 50 &
$ mpstat -P 6 1
CPU %usr %idle
Before 6 69.74 30.26
After 6 48.51 50.50
Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
Signed-off-by: Aboorva Devarajan <redacted>
Since the switch to generic entry, an interrupt from user mode
accounts user time twice: once in arch_interrupt_enter_prepare()
and again in arch_enter_from_user_mode(), which irqentry_enter()
invokes for the same interrupt:
arch_interrupt_enter_prepare()
account_cpu_user_entry() /* first */
irqentry_enter()
arch_enter_from_user_mode()
account_cpu_user_entry() /* second */
The second call charges the same interval again, because
account_cpu_user_entry() accumulates the time spent in user mode
since the last return to user space.
The two calls come from the GENERIC_ENTRY preparation series,
where each step was a no-op on its own. Commit 09a9d3a8499d
("powerpc: introduce arch_enter_from_user_mode") added the hook
with the user-time accounting in it, but nothing called it yet.
Commit 893082ac769b ("powerpc: Prepare for IRQ entry exit")
copied interrupt_enter_prepare() verbatim into entry-common.h as
arch_interrupt_enter_prepare(); that copy was equally unused, as
handlers still called interrupt_enter_prepare().
Commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
made both live. On the syscall side it did the full conversion:
system_call_exception() now accounts once through the hook via
syscall_enter_from_user_mode(), rather than calling
account_cpu_user_entry() directly. On the interrupt side it
switched the handler macros to arch_interrupt_enter_prepare()
followed by irqentry_enter(), which also runs the hook, but the
accounting in arch_interrupt_enter_prepare() was not removed to
match. The double accounting starts with that commit.
With CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y this roughly doubles the
reported user time of any workload that takes interrupts. The
other accounting modes compile account_cpu_user_entry() to an
empty stub, so they are not affected.
Remove the accounting from arch_interrupt_enter_prepare() and rely
on arch_enter_from_user_mode(), which already runs for both
syscalls and interrupts. The duplicate account_stolen_time() call
is removed the same way.
On a pseries LPAR a busy loop reports 6s user time in 3s elapsed
(~210% CPU) before the fix, and 3s (~105% CPU) after it:
$ python3 -c 'while True: pass' &
$ sleep 3; ps -p $! -o etime,time,pcpu
ELAPSED TIME %CPU
Before 00:03 00:00:06 210
After 00:03 00:00:03 105
A 50% load reports ~70% usr / 30% idle before the fix, and
~49% usr / 51% idle after it:
$ taskset -c 6 stress-ng --cpu 1 --cpu-load 50 &
$ mpstat -P 6 1
CPU %usr %idle
Before 6 69.74 30.26
After 6 48.51 50.50
Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
Signed-off-by: Aboorva Devarajan <redacted>
---
Looks good. Thanks for the descritive commit msg!
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
From: Amit Machhiwal <hidden> Date: 2026-09-06 09:03:52
On 2026/09/04 08:28 AM, Aboorva Devarajan wrote:
Since the switch to generic entry, an interrupt from user mode
accounts user time twice: once in arch_interrupt_enter_prepare()
and again in arch_enter_from_user_mode(), which irqentry_enter()
invokes for the same interrupt:
arch_interrupt_enter_prepare()
account_cpu_user_entry() /* first */
irqentry_enter()
arch_enter_from_user_mode()
account_cpu_user_entry() /* second */
The second call charges the same interval again, because
account_cpu_user_entry() accumulates the time spent in user mode
since the last return to user space.
The two calls come from the GENERIC_ENTRY preparation series,
where each step was a no-op on its own. Commit 09a9d3a8499d
("powerpc: introduce arch_enter_from_user_mode") added the hook
with the user-time accounting in it, but nothing called it yet.
Commit 893082ac769b ("powerpc: Prepare for IRQ entry exit")
copied interrupt_enter_prepare() verbatim into entry-common.h as
arch_interrupt_enter_prepare(); that copy was equally unused, as
handlers still called interrupt_enter_prepare().
Commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
made both live. On the syscall side it did the full conversion:
system_call_exception() now accounts once through the hook via
syscall_enter_from_user_mode(), rather than calling
account_cpu_user_entry() directly. On the interrupt side it
switched the handler macros to arch_interrupt_enter_prepare()
followed by irqentry_enter(), which also runs the hook, but the
accounting in arch_interrupt_enter_prepare() was not removed to
match. The double accounting starts with that commit.
With CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y this roughly doubles the
reported user time of any workload that takes interrupts. The
other accounting modes compile account_cpu_user_entry() to an
empty stub, so they are not affected.
Remove the accounting from arch_interrupt_enter_prepare() and rely
on arch_enter_from_user_mode(), which already runs for both
syscalls and interrupts. The duplicate account_stolen_time() call
is removed the same way.
On a pseries LPAR a busy loop reports 6s user time in 3s elapsed
(~210% CPU) before the fix, and 3s (~105% CPU) after it:
$ python3 -c 'while True: pass' &
$ sleep 3; ps -p $! -o etime,time,pcpu
ELAPSED TIME %CPU
Before 00:03 00:00:06 210
After 00:03 00:00:03 105
A 50% load reports ~70% usr / 30% idle before the fix, and
~49% usr / 51% idle after it:
$ taskset -c 6 stress-ng --cpu 1 --cpu-load 50 &
$ mpstat -P 6 1
CPU %usr %idle
Before 6 69.74 30.26
After 6 48.51 50.50
Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
Signed-off-by: Aboorva Devarajan <redacted>
The fix is minimal and correct: removing the two lines from
arch_interrupt_enter_prepare() leaves arch_enter_from_user_mode() as the single
accounting site for both syscalls and interrupts, which matches the generic
entry design intent. The benchmarks in the commit message are convincing.
Reviewed-by: Amit Machhiwal <redacted>
Thanks,
Amit
On 4 Sep 2026, at 8:28 AM, Aboorva Devarajan [off-list ref] wrote:
Since the switch to generic entry, an interrupt from user mode
accounts user time twice: once in arch_interrupt_enter_prepare()
and again in arch_enter_from_user_mode(), which irqentry_enter()
invokes for the same interrupt:
arch_interrupt_enter_prepare()
account_cpu_user_entry() /* first */
irqentry_enter()
arch_enter_from_user_mode()
account_cpu_user_entry() /* second */
The second call charges the same interval again, because
account_cpu_user_entry() accumulates the time spent in user mode
since the last return to user space.
The two calls come from the GENERIC_ENTRY preparation series,
where each step was a no-op on its own. Commit 09a9d3a8499d
("powerpc: introduce arch_enter_from_user_mode") added the hook
with the user-time accounting in it, but nothing called it yet.
Commit 893082ac769b ("powerpc: Prepare for IRQ entry exit")
copied interrupt_enter_prepare() verbatim into entry-common.h as
arch_interrupt_enter_prepare(); that copy was equally unused, as
handlers still called interrupt_enter_prepare().
Commit bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
made both live. On the syscall side it did the full conversion:
system_call_exception() now accounts once through the hook via
syscall_enter_from_user_mode(), rather than calling
account_cpu_user_entry() directly. On the interrupt side it
switched the handler macros to arch_interrupt_enter_prepare()
followed by irqentry_enter(), which also runs the hook, but the
accounting in arch_interrupt_enter_prepare() was not removed to
match. The double accounting starts with that commit.
With CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y this roughly doubles the
reported user time of any workload that takes interrupts. The
other accounting modes compile account_cpu_user_entry() to an
empty stub, so they are not affected.
Remove the accounting from arch_interrupt_enter_prepare() and rely
on arch_enter_from_user_mode(), which already runs for both
syscalls and interrupts. The duplicate account_stolen_time() call
is removed the same way.
On a pseries LPAR a busy loop reports 6s user time in 3s elapsed
(~210% CPU) before the fix, and 3s (~105% CPU) after it:
$ python3 -c 'while True: pass' &
$ sleep 3; ps -p $! -o etime,time,pcpu
ELAPSED TIME %CPU
Before 00:03 00:00:06 210
After 00:03 00:00:03 105
A 50% load reports ~70% usr / 30% idle before the fix, and
~49% usr / 51% idle after it:
$ taskset -c 6 stress-ng --cpu 1 --cpu-load 50 &
$ mpstat -P 6 1
CPU %usr %idle
Before 6 69.74 30.26
After 6 48.51 50.50
Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <redacted>
Signed-off-by: Aboorva Devarajan <redacted>
---
I have tested this patch, by applying on top of latest mainline, and its working as expected.
Please add below tag.
Tested-by: Venkat Rao Bagalkote <redacted>
Regards,
Venkat.
On Fri, 04 Sep 2026 08:28:30 +0530, Aboorva Devarajan wrote:
Since the switch to generic entry, an interrupt from user mode
accounts user time twice: once in arch_interrupt_enter_prepare()
and again in arch_enter_from_user_mode(), which irqentry_enter()
invokes for the same interrupt:
arch_interrupt_enter_prepare()
account_cpu_user_entry() /* first */
irqentry_enter()
arch_enter_from_user_mode()
account_cpu_user_entry() /* second */
[...]