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 <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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;
 }
 

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
 

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