* [PATCH 1/3] entry: move exit to usermode functions to header file
2023-12-05 13:30 [PATCH 0/3] entry: inline syscall enter/exit functions Sven Schnelle
@ 2023-12-05 13:30 ` Sven Schnelle
2023-12-15 19:09 ` Thomas Gleixner
2023-12-05 13:30 ` [PATCH 2/3] move enter_from_user_mode() " Sven Schnelle
` (2 subsequent siblings)
3 siblings, 1 reply; 10+ messages in thread
From: Sven Schnelle @ 2023-12-05 13:30 UTC (permalink / raw)
To: Thomas Gleixner, Peter Zijlstra, Andy Lutomirski
Cc: linux-kernel, Heiko Carstens
To allow inlining, move exit_to_user_mode() and
exit_to_user_mode_loop() to common.h.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
include/linux/entry-common.h | 95 +++++++++++++++++++++++++++++++++++-
kernel/entry/common.c | 89 +--------------------------------
2 files changed, 96 insertions(+), 88 deletions(-)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index d95ab85f96ba..f0f1a26dc638 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -7,6 +7,10 @@
#include <linux/syscalls.h>
#include <linux/seccomp.h>
#include <linux/sched.h>
+#include <linux/context_tracking.h>
+#include <linux/livepatch.h>
+#include <linux/resume_user_mode.h>
+#include <linux/tick.h>
#include <asm/entry-common.h>
@@ -258,6 +262,85 @@ static __always_inline void arch_exit_to_user_mode(void) { }
*/
void arch_do_signal_or_restart(struct pt_regs *regs);
+/**
+ * exit_to_user_mode_loop - do any pending work before leaving to user space
+ */
+static __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
+ unsigned long ti_work)
+{
+ /*
+ * Before returning to user space ensure that all pending work
+ * items have been completed.
+ */
+ while (ti_work & EXIT_TO_USER_MODE_WORK) {
+
+ local_irq_enable_exit_to_user(ti_work);
+
+ if (ti_work & _TIF_NEED_RESCHED)
+ schedule();
+
+ if (ti_work & _TIF_UPROBE)
+ uprobe_notify_resume(regs);
+
+ if (ti_work & _TIF_PATCH_PENDING)
+ klp_update_patch_state(current);
+
+ if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
+ arch_do_signal_or_restart(regs);
+
+ if (ti_work & _TIF_NOTIFY_RESUME)
+ resume_user_mode_work(regs);
+
+ /* Architecture specific TIF work */
+ arch_exit_to_user_mode_work(regs, ti_work);
+
+ /*
+ * Disable interrupts and reevaluate the work flags as they
+ * might have changed while interrupts and preemption was
+ * enabled above.
+ */
+ local_irq_disable_exit_to_user();
+
+ /* Check if any of the above work has queued a deferred wakeup */
+ tick_nohz_user_enter_prepare();
+
+ ti_work = read_thread_flags();
+ }
+
+ /* Return the latest work state for arch_exit_to_user_mode() */
+ return ti_work;
+}
+
+/**
+ * exit_to_user_mode_prepare - call exit_to_user_mode_loop() if required
+ *
+ * 1) check that interrupts are disabled
+ * 2) call tick_nohz_user_enter_prepare()
+ * 3) call exit_to_user_mode_loop() if any flags from
+ * EXIT_TO_USER_MODE_WORK are set
+ * 4) check that interrupts are still disabled
+ */
+static __always_inline void exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+ unsigned long ti_work;
+
+ lockdep_assert_irqs_disabled();
+
+ /* Flush pending rcuog wakeup before the last need_resched() check */
+ tick_nohz_user_enter_prepare();
+
+ ti_work = read_thread_flags();
+ if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
+ ti_work = exit_to_user_mode_loop(regs, ti_work);
+
+ arch_exit_to_user_mode_prepare(regs, ti_work);
+
+ /* Ensure that kernel state is sane for a return to userspace */
+ kmap_assert_nomap();
+ lockdep_assert_irqs_disabled();
+ lockdep_sys_exit();
+}
+
/**
* exit_to_user_mode - Fixup state when exiting to user mode
*
@@ -276,7 +359,17 @@ void arch_do_signal_or_restart(struct pt_regs *regs);
* non-instrumentable.
* The caller has to invoke syscall_exit_to_user_mode_work() before this.
*/
-void exit_to_user_mode(void);
+static __always_inline void exit_to_user_mode(void)
+{
+ instrumentation_begin();
+ trace_hardirqs_on_prepare();
+ lockdep_hardirqs_on_prepare();
+ instrumentation_end();
+
+ user_enter_irqoff();
+ arch_exit_to_user_mode();
+ lockdep_hardirqs_on(CALLER_ADDR0);
+}
/**
* syscall_exit_to_user_mode_work - Handle work before returning to user mode
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d7ee4bc3f2ba..6ba2bcfbe32c 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -123,94 +123,9 @@ noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
instrumentation_end();
}
-/* See comment for exit_to_user_mode() in entry-common.h */
-static __always_inline void __exit_to_user_mode(void)
-{
- instrumentation_begin();
- trace_hardirqs_on_prepare();
- lockdep_hardirqs_on_prepare();
- instrumentation_end();
-
- user_enter_irqoff();
- arch_exit_to_user_mode();
- lockdep_hardirqs_on(CALLER_ADDR0);
-}
-
-void noinstr exit_to_user_mode(void)
-{
- __exit_to_user_mode();
-}
-
/* Workaround to allow gradual conversion of architecture code */
void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
-static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
- unsigned long ti_work)
-{
- /*
- * Before returning to user space ensure that all pending work
- * items have been completed.
- */
- while (ti_work & EXIT_TO_USER_MODE_WORK) {
-
- local_irq_enable_exit_to_user(ti_work);
-
- if (ti_work & _TIF_NEED_RESCHED)
- schedule();
-
- if (ti_work & _TIF_UPROBE)
- uprobe_notify_resume(regs);
-
- if (ti_work & _TIF_PATCH_PENDING)
- klp_update_patch_state(current);
-
- if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
- arch_do_signal_or_restart(regs);
-
- if (ti_work & _TIF_NOTIFY_RESUME)
- resume_user_mode_work(regs);
-
- /* Architecture specific TIF work */
- arch_exit_to_user_mode_work(regs, ti_work);
-
- /*
- * Disable interrupts and reevaluate the work flags as they
- * might have changed while interrupts and preemption was
- * enabled above.
- */
- local_irq_disable_exit_to_user();
-
- /* Check if any of the above work has queued a deferred wakeup */
- tick_nohz_user_enter_prepare();
-
- ti_work = read_thread_flags();
- }
-
- /* Return the latest work state for arch_exit_to_user_mode() */
- return ti_work;
-}
-
-static void exit_to_user_mode_prepare(struct pt_regs *regs)
-{
- unsigned long ti_work;
-
- lockdep_assert_irqs_disabled();
-
- /* Flush pending rcuog wakeup before the last need_resched() check */
- tick_nohz_user_enter_prepare();
-
- ti_work = read_thread_flags();
- if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
- ti_work = exit_to_user_mode_loop(regs, ti_work);
-
- arch_exit_to_user_mode_prepare(regs, ti_work);
-
- /* Ensure that kernel state is sane for a return to userspace */
- kmap_assert_nomap();
- lockdep_assert_irqs_disabled();
- lockdep_sys_exit();
-}
-
/*
* If SYSCALL_EMU is set, then the only reason to report is when
* SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
@@ -295,7 +210,7 @@ __visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
instrumentation_begin();
__syscall_exit_to_user_mode_work(regs);
instrumentation_end();
- __exit_to_user_mode();
+ exit_to_user_mode();
}
noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
@@ -308,7 +223,7 @@ noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
instrumentation_begin();
exit_to_user_mode_prepare(regs);
instrumentation_end();
- __exit_to_user_mode();
+ exit_to_user_mode();
}
noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
--
2.40.1
^ permalink raw reply related [flat|nested] 10+ messages in thread* Re: [PATCH 1/3] entry: move exit to usermode functions to header file
2023-12-05 13:30 ` [PATCH 1/3] entry: move exit to usermode functions to header file Sven Schnelle
@ 2023-12-15 19:09 ` Thomas Gleixner
2023-12-18 7:46 ` Sven Schnelle
0 siblings, 1 reply; 10+ messages in thread
From: Thomas Gleixner @ 2023-12-15 19:09 UTC (permalink / raw)
To: Sven Schnelle, Peter Zijlstra, Andy Lutomirski
Cc: linux-kernel, Heiko Carstens
On Tue, Dec 05 2023 at 14:30, Sven Schnelle wrote:
> +/**
> + * exit_to_user_mode_loop - do any pending work before leaving to user space
> + */
> +static __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
> + unsigned long ti_work)
> +{
> + /*
> + * Before returning to user space ensure that all pending work
> + * items have been completed.
> + */
> + while (ti_work & EXIT_TO_USER_MODE_WORK) {
> +
> + local_irq_enable_exit_to_user(ti_work);
> +
> + if (ti_work & _TIF_NEED_RESCHED)
> + schedule();
> +
> + if (ti_work & _TIF_UPROBE)
> + uprobe_notify_resume(regs);
> +
> + if (ti_work & _TIF_PATCH_PENDING)
> + klp_update_patch_state(current);
> +
> + if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> + arch_do_signal_or_restart(regs);
> +
> + if (ti_work & _TIF_NOTIFY_RESUME)
> + resume_user_mode_work(regs);
> +
> + /* Architecture specific TIF work */
> + arch_exit_to_user_mode_work(regs, ti_work);
> +
> + /*
> + * Disable interrupts and reevaluate the work flags as they
> + * might have changed while interrupts and preemption was
> + * enabled above.
> + */
> + local_irq_disable_exit_to_user();
> +
> + /* Check if any of the above work has queued a deferred wakeup */
> + tick_nohz_user_enter_prepare();
> +
> + ti_work = read_thread_flags();
> + }
> +
> + /* Return the latest work state for arch_exit_to_user_mode() */
> + return ti_work;
> +}
I'm not really sure about this part. exit_to_user_mode_loop() is the
slowpath when a TIF work flag is set. I can see the benefit on the
fastpath functions which are way smaller.
Thanks,
tglx
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 1/3] entry: move exit to usermode functions to header file
2023-12-15 19:09 ` Thomas Gleixner
@ 2023-12-18 7:46 ` Sven Schnelle
0 siblings, 0 replies; 10+ messages in thread
From: Sven Schnelle @ 2023-12-18 7:46 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Peter Zijlstra, Andy Lutomirski, linux-kernel, Heiko Carstens
Hi Thomas,
Thomas Gleixner <tglx@linutronix.de> writes:
> On Tue, Dec 05 2023 at 14:30, Sven Schnelle wrote:
>> +/**
>> + * exit_to_user_mode_loop - do any pending work before leaving to user space
>> + */
>> +static __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
>> + unsigned long ti_work)
>> +{
>> + /*
>> + * Before returning to user space ensure that all pending work
>> + * items have been completed.
>> + */
>> + while (ti_work & EXIT_TO_USER_MODE_WORK) {
>> +
>> + local_irq_enable_exit_to_user(ti_work);
>> +
>> + if (ti_work & _TIF_NEED_RESCHED)
>> + schedule();
>> +
>> + if (ti_work & _TIF_UPROBE)
>> + uprobe_notify_resume(regs);
>> +
>> + if (ti_work & _TIF_PATCH_PENDING)
>> + klp_update_patch_state(current);
>> +
>> + if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
>> + arch_do_signal_or_restart(regs);
>> +
>> + if (ti_work & _TIF_NOTIFY_RESUME)
>> + resume_user_mode_work(regs);
>> +
>> + /* Architecture specific TIF work */
>> + arch_exit_to_user_mode_work(regs, ti_work);
>> +
>> + /*
>> + * Disable interrupts and reevaluate the work flags as they
>> + * might have changed while interrupts and preemption was
>> + * enabled above.
>> + */
>> + local_irq_disable_exit_to_user();
>> +
>> + /* Check if any of the above work has queued a deferred wakeup */
>> + tick_nohz_user_enter_prepare();
>> +
>> + ti_work = read_thread_flags();
>> + }
>> +
>> + /* Return the latest work state for arch_exit_to_user_mode() */
>> + return ti_work;
>> +}
>
> I'm not really sure about this part. exit_to_user_mode_loop() is the
> slowpath when a TIF work flag is set. I can see the benefit on the
> fastpath functions which are way smaller.
Indeed, the main performance improvement comes from inlining the small
functions. As Peter mentioned the same, i sent out a v2 which doesn't
move exit_to_user_mode_loop().
Thanks!
Sven
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 2/3] move enter_from_user_mode() to header file
2023-12-05 13:30 [PATCH 0/3] entry: inline syscall enter/exit functions Sven Schnelle
2023-12-05 13:30 ` [PATCH 1/3] entry: move exit to usermode functions to header file Sven Schnelle
@ 2023-12-05 13:30 ` Sven Schnelle
2023-12-05 13:30 ` [PATCH 3/3] entry: move syscall_enter_from_user_mode() " Sven Schnelle
2023-12-06 11:02 ` [PATCH 0/3] entry: inline syscall enter/exit functions Peter Zijlstra
3 siblings, 0 replies; 10+ messages in thread
From: Sven Schnelle @ 2023-12-05 13:30 UTC (permalink / raw)
To: Thomas Gleixner, Peter Zijlstra, Andy Lutomirski
Cc: linux-kernel, Heiko Carstens
To allow inlining of enter_from_user_mode(), move it to common.h.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
include/linux/entry-common.h | 15 ++++++++++++++-
kernel/entry/common.c | 26 +++-----------------------
2 files changed, 17 insertions(+), 24 deletions(-)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index f0f1a26dc638..e2c62d111318 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -11,6 +11,7 @@
#include <linux/livepatch.h>
#include <linux/resume_user_mode.h>
#include <linux/tick.h>
+#include <linux/kmsan.h>
#include <asm/entry-common.h>
@@ -102,7 +103,19 @@ static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs) {}
* done between establishing state and enabling interrupts. The caller must
* enable interrupts before invoking syscall_enter_from_user_mode_work().
*/
-void enter_from_user_mode(struct pt_regs *regs);
+static __always_inline void enter_from_user_mode(struct pt_regs *regs)
+{
+ arch_enter_from_user_mode(regs);
+ lockdep_hardirqs_off(CALLER_ADDR0);
+
+ CT_WARN_ON(__ct_state() != CONTEXT_USER);
+ user_exit_irqoff();
+
+ instrumentation_begin();
+ kmsan_unpoison_entry_regs(regs);
+ trace_hardirqs_off_finish();
+ instrumentation_end();
+}
/**
* syscall_enter_from_user_mode_prepare - Establish state and enable interrupts
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 6ba2bcfbe32c..90b995facd7a 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -15,26 +15,6 @@
#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
-/* See comment for enter_from_user_mode() in entry-common.h */
-static __always_inline void __enter_from_user_mode(struct pt_regs *regs)
-{
- arch_enter_from_user_mode(regs);
- lockdep_hardirqs_off(CALLER_ADDR0);
-
- CT_WARN_ON(__ct_state() != CONTEXT_USER);
- user_exit_irqoff();
-
- instrumentation_begin();
- kmsan_unpoison_entry_regs(regs);
- trace_hardirqs_off_finish();
- instrumentation_end();
-}
-
-void noinstr enter_from_user_mode(struct pt_regs *regs)
-{
- __enter_from_user_mode(regs);
-}
-
static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
{
if (unlikely(audit_context())) {
@@ -105,7 +85,7 @@ noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
{
long ret;
- __enter_from_user_mode(regs);
+ enter_from_user_mode(regs);
instrumentation_begin();
local_irq_enable();
@@ -117,7 +97,7 @@ noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
{
- __enter_from_user_mode(regs);
+ enter_from_user_mode(regs);
instrumentation_begin();
local_irq_enable();
instrumentation_end();
@@ -215,7 +195,7 @@ __visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
{
- __enter_from_user_mode(regs);
+ enter_from_user_mode(regs);
}
noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
--
2.40.1
^ permalink raw reply related [flat|nested] 10+ messages in thread* [PATCH 3/3] entry: move syscall_enter_from_user_mode() to header file
2023-12-05 13:30 [PATCH 0/3] entry: inline syscall enter/exit functions Sven Schnelle
2023-12-05 13:30 ` [PATCH 1/3] entry: move exit to usermode functions to header file Sven Schnelle
2023-12-05 13:30 ` [PATCH 2/3] move enter_from_user_mode() " Sven Schnelle
@ 2023-12-05 13:30 ` Sven Schnelle
2023-12-06 11:02 ` [PATCH 0/3] entry: inline syscall enter/exit functions Peter Zijlstra
3 siblings, 0 replies; 10+ messages in thread
From: Sven Schnelle @ 2023-12-05 13:30 UTC (permalink / raw)
To: Thomas Gleixner, Peter Zijlstra, Andy Lutomirski
Cc: linux-kernel, Heiko Carstens
To allow inlining of syscall_enter_from_user_mode(), move it
to the entry-common.h header file.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
include/linux/entry-common.h | 27 +++++++++++++++++++++++++--
kernel/entry/common.c | 32 +-------------------------------
2 files changed, 26 insertions(+), 33 deletions(-)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index e2c62d111318..ed26d626d587 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -134,6 +134,9 @@ static __always_inline void enter_from_user_mode(struct pt_regs *regs)
*/
void syscall_enter_from_user_mode_prepare(struct pt_regs *regs);
+long syscall_trace_enter(struct pt_regs *regs, long syscall,
+ unsigned long work);
+
/**
* syscall_enter_from_user_mode_work - Check and handle work before invoking
* a syscall
@@ -157,7 +160,15 @@ void syscall_enter_from_user_mode_prepare(struct pt_regs *regs);
* ptrace_report_syscall_entry(), __secure_computing(), trace_sys_enter()
* 2) Invocation of audit_syscall_entry()
*/
-long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall);
+static __always_inline long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall)
+{
+ unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
+
+ if (work & SYSCALL_WORK_ENTER)
+ syscall = syscall_trace_enter(regs, syscall, work);
+
+ return syscall;
+}
/**
* syscall_enter_from_user_mode - Establish state and check and handle work
@@ -176,7 +187,19 @@ long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall);
* Returns: The original or a modified syscall number. See
* syscall_enter_from_user_mode_work() for further explanation.
*/
-long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall);
+static __always_inline long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
+{
+ long ret;
+
+ enter_from_user_mode(regs);
+
+ instrumentation_begin();
+ local_irq_enable();
+ ret = syscall_enter_from_user_mode_work(regs, syscall);
+ instrumentation_end();
+
+ return ret;
+}
/**
* local_irq_enable_exit_to_user - Exit to user variant of local_irq_enable()
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 90b995facd7a..dde4a9c1f9f3 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -25,7 +25,7 @@ static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
}
}
-static long syscall_trace_enter(struct pt_regs *regs, long syscall,
+long syscall_trace_enter(struct pt_regs *regs, long syscall,
unsigned long work)
{
long ret = 0;
@@ -65,36 +65,6 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
return ret ? : syscall;
}
-static __always_inline long
-__syscall_enter_from_user_work(struct pt_regs *regs, long syscall)
-{
- unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
-
- if (work & SYSCALL_WORK_ENTER)
- syscall = syscall_trace_enter(regs, syscall, work);
-
- return syscall;
-}
-
-long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall)
-{
- return __syscall_enter_from_user_work(regs, syscall);
-}
-
-noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
-{
- long ret;
-
- enter_from_user_mode(regs);
-
- instrumentation_begin();
- local_irq_enable();
- ret = __syscall_enter_from_user_work(regs, syscall);
- instrumentation_end();
-
- return ret;
-}
-
noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
{
enter_from_user_mode(regs);
--
2.40.1
^ permalink raw reply related [flat|nested] 10+ messages in thread* Re: [PATCH 0/3] entry: inline syscall enter/exit functions
2023-12-05 13:30 [PATCH 0/3] entry: inline syscall enter/exit functions Sven Schnelle
` (2 preceding siblings ...)
2023-12-05 13:30 ` [PATCH 3/3] entry: move syscall_enter_from_user_mode() " Sven Schnelle
@ 2023-12-06 11:02 ` Peter Zijlstra
2023-12-14 8:24 ` Sven Schnelle
3 siblings, 1 reply; 10+ messages in thread
From: Peter Zijlstra @ 2023-12-06 11:02 UTC (permalink / raw)
To: Sven Schnelle
Cc: Thomas Gleixner, Andy Lutomirski, linux-kernel, Heiko Carstens
On Tue, Dec 05, 2023 at 02:30:12PM +0100, Sven Schnelle wrote:
> Hi List,
>
> looking into the performance of syscall entry/exit after s390 switched
> to generic entry showed that there's quite some overhead calling some
> of the entry/exit work functions even when there's nothing to do.
> This patchset moves the entry and exit function to entry-common.h, so
> non inlined code gets only called when there is some work pending.
So per that logic you wouldn't need to inline exit_to_user_mode_loop()
for example, that's only called when there is a EXIT_TO_USER_MODE_WORK
bit set.
That is, I'm just being pedantic here and pointing out that your
justification doesn't cover the extent of the changes.
> I wrote a small program that just issues invalid syscalls in a loop.
> On an s390 machine, this results in the following numbers:
>
> without this series:
>
> # ./syscall 1000000000
> runtime: 94.886581s / per-syscall 9.488658e-08s
>
> with this series:
>
> ./syscall 1000000000
> runtime: 84.732391s / per-syscall 8.473239e-08s
>
> so the time required for one syscall dropped from 94.8ns to
> 84.7ns, which is a drop of about 11%.
That is obviously very nice, and I don't immediately see anything wrong
with moving the lot to header based inlines.
Thomas?
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH 0/3] entry: inline syscall enter/exit functions
2023-12-06 11:02 ` [PATCH 0/3] entry: inline syscall enter/exit functions Peter Zijlstra
@ 2023-12-14 8:24 ` Sven Schnelle
2023-12-15 19:06 ` Thomas Gleixner
0 siblings, 1 reply; 10+ messages in thread
From: Sven Schnelle @ 2023-12-14 8:24 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Peter Zijlstra, Andy Lutomirski, linux-kernel, Heiko Carstens
Peter Zijlstra <peterz@infradead.org> writes:
> On Tue, Dec 05, 2023 at 02:30:12PM +0100, Sven Schnelle wrote:
>> Hi List,
>>
>> looking into the performance of syscall entry/exit after s390 switched
>> to generic entry showed that there's quite some overhead calling some
>> of the entry/exit work functions even when there's nothing to do.
>> This patchset moves the entry and exit function to entry-common.h, so
>> non inlined code gets only called when there is some work pending.
>
> So per that logic you wouldn't need to inline exit_to_user_mode_loop()
> for example, that's only called when there is a EXIT_TO_USER_MODE_WORK
> bit set.
>
> That is, I'm just being pedantic here and pointing out that your
> justification doesn't cover the extent of the changes.
>
>> I wrote a small program that just issues invalid syscalls in a loop.
>> On an s390 machine, this results in the following numbers:
>>
>> without this series:
>>
>> # ./syscall 1000000000
>> runtime: 94.886581s / per-syscall 9.488658e-08s
>>
>> with this series:
>>
>> ./syscall 1000000000
>> runtime: 84.732391s / per-syscall 8.473239e-08s
>>
>> so the time required for one syscall dropped from 94.8ns to
>> 84.7ns, which is a drop of about 11%.
>
> That is obviously very nice, and I don't immediately see anything wrong
> with moving the lot to header based inlines.
>
> Thomas?
Thomas, any opinion on this change?
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 0/3] entry: inline syscall enter/exit functions
2023-12-14 8:24 ` Sven Schnelle
@ 2023-12-15 19:06 ` Thomas Gleixner
0 siblings, 0 replies; 10+ messages in thread
From: Thomas Gleixner @ 2023-12-15 19:06 UTC (permalink / raw)
To: Sven Schnelle
Cc: Peter Zijlstra, Andy Lutomirski, linux-kernel, Heiko Carstens
On Thu, Dec 14 2023 at 09:24, Sven Schnelle wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
>>> so the time required for one syscall dropped from 94.8ns to
>>> 84.7ns, which is a drop of about 11%.
>>
>> That is obviously very nice, and I don't immediately see anything wrong
>> with moving the lot to header based inlines.
>>
>> Thomas?
No objections in principle. Let me look at the lot
^ permalink raw reply [flat|nested] 10+ messages in thread