From 8b0b1db0133e4218a9b45c09e53793c039edebe1 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 16 Jun 2009 15:33:39 -0700 Subject: [PATCH] remove put_cpu_no_resched() 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 [akpm@linux-foundation.org: build fix] Signed-off-by: Thomas Gleixner Acked-by: Ingo Molnar Cc: Tony Luck Cc: Trond Myklebust Cc: "J. Bruce Fields" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/ia64/kernel/perfmon.c | 2 +- fs/nfs/iostat.h | 6 +++--- include/linux/smp.h | 1 - 3 files changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/ia64/kernel/perfmon.c b/arch/ia64/kernel/perfmon.c index 8a06dc480594..bdc176cb5e85 100644 --- a/arch/ia64/kernel/perfmon.c +++ b/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 --git a/fs/nfs/iostat.h b/fs/nfs/iostat.h index a2ab2529b5ca..ceda50aad73c 100644 --- a/fs/nfs/iostat.h +++ b/fs/nfs/iostat.h @@ -31,7 +31,7 @@ static inline void nfs_inc_server_stats(const struct nfs_server *server, 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(const struct nfs_server *server, 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, @@ -71,7 +71,7 @@ static inline void nfs_add_fscache_stats(struct inode *inode, cpu = get_cpu(); iostats = per_cpu_ptr(NFS_SERVER(inode)->io_stats, cpu); iostats->fscache[stat] += addend; - put_cpu_no_resched(); + put_cpu(); } #endif diff --git a/include/linux/smp.h b/include/linux/smp.h index a69db820eed6..9e3d8af09207 100644 --- a/include/linux/smp.h +++ b/include/linux/smp.h @@ -177,7 +177,6 @@ static inline void init_call_single_data(void) #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 -- 2.20.1