* + smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch added to mm-nonmm-unstable branch
@ 2022-08-24 18:26 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2022-08-24 18:26 UTC (permalink / raw)
To: mm-commits, ubizjak, akpm
The patch titled
Subject: smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death
has been added to the -mm mm-nonmm-unstable branch. Its filename is
smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
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c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Uros Bizjak <ubizjak@gmail.com>
Subject: smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death
Date: Tue, 23 Aug 2022 17:13:36 +0200
Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in cpu_wait_death and cpu_report_death. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg).
Also, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when
cmpxchg fails, enabling further code simplifications.
No functional change intended.
Link: https://lkml.kernel.org/r/20220823151336.3984-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
kernel/smpboot.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/kernel/smpboot.c~smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death
+++ a/kernel/smpboot.c
@@ -444,16 +444,16 @@ bool cpu_wait_death(unsigned int cpu, in
break;
sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
}
-update_state:
oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
+update_state:
if (oldstate == CPU_DEAD) {
/* Outgoing CPU died normally, update state. */
smp_mb(); /* atomic_read() before update. */
atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
} else {
/* Outgoing CPU still hasn't died, set state accordingly. */
- if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
- oldstate, CPU_BROKEN) != oldstate)
+ if (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
+ &oldstate, CPU_BROKEN))
goto update_state;
ret = false;
}
@@ -475,14 +475,14 @@ bool cpu_report_death(void)
int newstate;
int cpu = smp_processor_id();
+ oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
do {
- oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
if (oldstate != CPU_BROKEN)
newstate = CPU_DEAD;
else
newstate = CPU_DEAD_FROZEN;
- } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
- oldstate, newstate) != oldstate);
+ } while (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
+ &oldstate, newstate));
return newstate == CPU_DEAD;
}
_
Patches currently in -mm which might be from ubizjak@gmail.com are
llist-use-try_cmpxchg-in-llist_add_batch-and-llist_del_first.patch
epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch
buffer-use-try_cmpxchg-in-discard_buffer.patch
aio-use-atomic_try_cmpxchg-in-__get_reqs_available.patch
iversion-use-atomic64_try_cmpxchg.patch
bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch
task_work-use-try_cmpxchg-in-task_work_add-task_work_cancel_match-and-task_work_run.patch
smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
* + smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch added to mm-nonmm-unstable branch
@ 2022-08-26 1:54 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2022-08-26 1:54 UTC (permalink / raw)
To: mm-commits, ubizjak, akpm
The patch titled
Subject: smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death
has been added to the -mm mm-nonmm-unstable branch. Its filename is
smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Uros Bizjak <ubizjak@gmail.com>
Subject: smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death
Date: Thu, 25 Aug 2022 16:56:03 +0200
Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in cpu_wait_death and cpu_report_death. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg). Also, atomic_try_cmpxchg
implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling
further code simplifications.
No functional change intended.
Link: https://lkml.kernel.org/r/20220825145603.5811-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
kernel/smpboot.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
--- a/kernel/smpboot.c~smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death
+++ a/kernel/smpboot.c
@@ -433,7 +433,7 @@ bool cpu_wait_death(unsigned int cpu, in
/* The outgoing CPU will normally get done quite quickly. */
if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
- goto update_state;
+ goto update_state_early;
udelay(5);
/* But if the outgoing CPU dawdles, wait increasingly long times. */
@@ -444,16 +444,17 @@ bool cpu_wait_death(unsigned int cpu, in
break;
sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
}
-update_state:
+update_state_early:
oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
+update_state:
if (oldstate == CPU_DEAD) {
/* Outgoing CPU died normally, update state. */
smp_mb(); /* atomic_read() before update. */
atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
} else {
/* Outgoing CPU still hasn't died, set state accordingly. */
- if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
- oldstate, CPU_BROKEN) != oldstate)
+ if (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
+ &oldstate, CPU_BROKEN))
goto update_state;
ret = false;
}
@@ -475,14 +476,14 @@ bool cpu_report_death(void)
int newstate;
int cpu = smp_processor_id();
+ oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
do {
- oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
if (oldstate != CPU_BROKEN)
newstate = CPU_DEAD;
else
newstate = CPU_DEAD_FROZEN;
- } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
- oldstate, newstate) != oldstate);
+ } while (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
+ &oldstate, newstate));
return newstate == CPU_DEAD;
}
_
Patches currently in -mm which might be from ubizjak@gmail.com are
llist-use-try_cmpxchg-in-llist_add_batch-and-llist_del_first.patch
epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch
buffer-use-try_cmpxchg-in-discard_buffer.patch
aio-use-atomic_try_cmpxchg-in-__get_reqs_available.patch
iversion-use-atomic64_try_cmpxchg.patch
bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch
task_work-use-try_cmpxchg-in-task_work_add-task_work_cancel_match-and-task_work_run.patch
smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch
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