The patch titled
remove put_cpu_no_resched()
has been added to the -mm tree. Its filename is
remove-put_cpu_no_resched.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: remove put_cpu_no_resched()
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
put_cpu_no_resched() is an optimization of put_cpu() which unfortunately
can cause high latencies.
The nfs iostats code uses put_cpu_no_resched() in a code sequence where a
reschedule request caused by an interrupt between the get_cpu() and the
put_cpu_no_resched() can delay the reschedule for at least HZ.
The other users of put_cpu_no_resched() optimize correctly in interrupt
code, but there is no real harm in using the put_cpu() function which is
an alias for preempt_enable(). The extra check of the preemmpt count is
not as critical as the potential source of missing a reschedule.
Debugged in the preempt-rt tree and verified in mainline.
Impact: remove a high latency source
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/ia64/kernel/perfmon.c | 2 +-
fs/nfs/iostat.h | 4 ++--
include/linux/smp.h | 1 -
3 files changed, 3 insertions(+), 4 deletions(-)
diff -puN arch/ia64/kernel/perfmon.c~remove-put_cpu_no_resched arch/ia64/kernel/perfmon.c
--- a/arch/ia64/kernel/perfmon.c~remove-put_cpu_no_resched
+++ a/arch/ia64/kernel/perfmon.c
@@ -5595,7 +5595,7 @@ pfm_interrupt_handler(int irq, void *arg
(*pfm_alt_intr_handler->handler)(irq, arg, regs);
}
- put_cpu_no_resched();
+ put_cpu();
return IRQ_HANDLED;
}
diff -puN fs/nfs/iostat.h~remove-put_cpu_no_resched fs/nfs/iostat.h
--- a/fs/nfs/iostat.h~remove-put_cpu_no_resched
+++ a/fs/nfs/iostat.h
@@ -31,7 +31,7 @@ static inline void nfs_inc_server_stats(
cpu = get_cpu();
iostats = per_cpu_ptr(server->io_stats, cpu);
iostats->events[stat]++;
- put_cpu_no_resched();
+ put_cpu();
}
static inline void nfs_inc_stats(const struct inode *inode,
@@ -50,7 +50,7 @@ static inline void nfs_add_server_stats(
cpu = get_cpu();
iostats = per_cpu_ptr(server->io_stats, cpu);
iostats->bytes[stat] += addend;
- put_cpu_no_resched();
+ put_cpu();
}
static inline void nfs_add_stats(const struct inode *inode,
diff -puN include/linux/smp.h~remove-put_cpu_no_resched include/linux/smp.h
--- a/include/linux/smp.h~remove-put_cpu_no_resched
+++ a/include/linux/smp.h
@@ -177,7 +177,6 @@ static inline void init_call_single_data
#define get_cpu() ({ preempt_disable(); smp_processor_id(); })
#define put_cpu() preempt_enable()
-#define put_cpu_no_resched() preempt_enable_no_resched()
/*
* Callback to arch code if there's nosmp or maxcpus=0 on the
_
Patches currently in -mm which might be from tglx@xxxxxxxxxxxxx are
linux-next.patch
arch-x86-kernel-cpu-cpufreq-acpi-cpufreqc-avoid-cross-cpu-interrupts.patch
x86-simplify-highmem-related-kconfig-entries.patch
x86-enable-gart-iommu-only-after-setting-up-protection-methods.patch
avr32-remove-obsolete-hw_interrupt_type.patch
kernel-time-tick-broadcastc-tick_broadcast_device-can-become-static.patch
timers-allow-deferrable-timers-for-intervals-tv2-tv5-to-be-deferred.patch
time-move-calc_load-call-out-from-xtime_lock-protection.patch
time-avoid-possible-endless-loop-when-using-jiffies-clocksource-and-oneshot-mode-clockevent.patch
clockevent-export-register_device-and-delta2ns.patch
clocksource-sanity-check-sysfs-clocksource-changes.patch
ia64-remove-obsolete-no_irq_type.patch
ia64-remove-obsolete-irq_desc_t-typedef.patch
ia64-remove-obsolete-hw_interrupt_type.patch
drivers-mfd-remove-obsolete-irq_desc_t-typedef.patch
parisc-remove-obsolete-hw_interrupt_type.patch
revert-genirq-assert-that-irq-handlers-are-indeed-running-in-hardirq-context.patch
alpha-remove-obsolete-hw_interrupt_type.patch
m32r-remove-obsolete-hw_interrupt_type.patch
um-remove-obsolete-hw_interrupt_type.patch
kmap_types-make-most-arches-use-generic-header-file.patch
remove-put_cpu_no_resched.patch
irqs-add-irqf_sample_random-to-the-feature-removal-scheduletxt-deprecated-list.patch
signals-split-do_tkill.patch
signals-implement-sys_rt_tgsigqueueinfo.patch
x86-hookup-sys_rt_tgsigqueueinfo.patch
--
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